Academic Appointments

Honors & Awards

  • Bing Prize for Excellence & Innovation in Undergraduate Teaching, Stanford University (1996-99)
  • Cox Medal for Excellence in Fostering Undergraduate Research, Stanford University (1998)
  • Dinkelspiel Prize for Outstanding Contributions to Undergraduate Education, Stanford University (2000)
  • Benjamin Scott Crocker Professor of Human Biology, Stanford University (1994-)
  • NIH Fogarty Senior International Fellowship, NIH (1985-86)
  • Javits Neuroscience Investigator Award, National Institute of Neurological Disorders and Stroke (1999-2006)
  • Fellow-American Association for Advancement of Science, AAAS (2003)
  • Rank Prize in Vision/Opto-electronics, Rank Foundation (February 2004)
  • Elected Fellow, American Academy of Arts and Sciences (2011)

Professional Education

  • PhD, University of Pennsylvania, Biophysics (1969)
  • B.S., Swarthmore College, Electrical Engineering/Physics (1963)

Current Research and Scholarly Interests

How does social experience influence the brain?
Our research is focused on understanding the mechanisms through which social change is transduced into cellular and molecular change. Sex is the most potent selective force acting on animal behavior, shaping many aspects of animals’ behavior and physiology. How is vertebrate sexual maturation and behavior controlled? Ultimately, males regulate reproductive opportunity and success through their behavior and social interactions, selecting a mate from among males on offer. Males use a variety of competitive strategies, evolved to impress females, intending to become the chosen one. Amongst males, there is typically a status hierarchy in which males compete for highest rank that brings with it a higher chance of being chosen because high status leads to reproductive opportunity and competence as well as access to females and food. Lower ranking animals often have limited access to food and reproduction and are reproductively incompetent. To understand the circuitry responsible for male reproduction, we study the neural mechanisms of social ascent, assessing the changes in males as they ascend from low to high status. We use a uniquely appropriate fish model system dominance is reflected in maintaining a territory so when a vacated territory becomes available, a low-ranking male must quickly detect his absence, seize the opportunity to acquire this valuable resource, and initiate a dramatic transformation that spans from whole-organism behavior and coloration changes, to hormonal, cellular, and transcriptional-level changes throughout the body. In fact, within a matter of minutes, his appearance and physiology has changed radically as he prepares for a new lifestyle as a dominant and reproductively active territory holder. But social ascent happens over two timescales. Following the rapid changes described above that occur in minutes, the reproductive system also needs to ramp up so the male has sperm for mating. Though both of these systems are triggered by the recognition of social opportunity, we can show that they comprise distinct circuits in which different neural peptides are activated to achieve the changes needed.

2016-17 Courses

Stanford Advisees

Graduate and Fellowship Programs

All Publications

  • Timing reproduction in teleost fish: cues and mechanisms CURRENT OPINION IN NEUROBIOLOGY Juntti, S. A., Fernald, R. D. 2016; 38: 57-62


    Fish comprise half of extant vertebrate species and use a rich variety of reproductive strategies that have yielded insights into the basic mechanisms that evolved for sex. To maximize the chances of fertilization and survival of offspring, fish species time reproduction to occur at optimal times. For years, ethologists have performed painstaking experiments to identify sensory inputs and behavioral outputs of the brain during mating. Here we review known mechanisms that generate sexual behavior, focusing on the factors that govern the timing of these displays. The development of new technologies, including high-throughput sequencing and genome engineering, has the potential to provide novel insights into how the vertebrate brain consummates mating at the appropriate time.

    View details for DOI 10.1016/j.conb.2016.02.006

    View details for Web of Science ID 000379556700010

    View details for PubMedID 26952366

  • A Neural Basis for Control of Cichlid Female Reproductive Behavior by Prostaglandin F-2 alpha CURRENT BIOLOGY Juntti, S. A., Hilliard, A. T., Kent, K. R., Kumar, A., Andrew Nguyen, A., Jimenez, M. A., Loveland, J. L., Mourrain, P., Fernald, R. D. 2016; 26 (7): 943-949
  • A Neural Basis for Control of Cichlid Female Reproductive Behavior by Prostaglandin F2a. Current biology Juntti, S. A., Hilliard, A. T., Kent, K. R., Kumar, A., Nguyen, A., Jimenez, M. A., Loveland, J. L., Mourrain, P., Fernald, R. D. 2016; 26 (7): 943-949


    In most species, females time reproduction to coincide with fertility. Thus, identifying factors that signal fertility to the brain can provide access to neural circuits that control sexual behaviors. In vertebrates, levels of key signaling molecules rise at the time of fertility to prime the brain for reproductive behavior [1-11], but how and where they regulate neural circuits is not known [12, 13]. Specifically, 17α,20β-dihydroxyprogesterone (DHP) and prostaglandin F2α (PGF2α) levels rise in teleost fish around the time of ovulation [10, 14, 15]. In an African cichlid fish, Astatotilapia burtoni, fertile females select a mate and perform a stereotyped spawning routine, offering quantifiable behavioral outputs of neural circuits. We show that, within minutes, PGF2α injection activates a naturalistic pattern of sexual behavior in female A. burtoni. We also identify cells in the brain that transduce the prostaglandin signal to mate and show that the gonadal steroid DHP modulates mRNA levels of the putative receptor for PGF2α (Ptgfr). We use CRISPR/Cas9 to generate the first targeted gene mutation in A. burtoni and show that Ptgfr is necessary for the initiation of sexual behavior, uncoupling sexual behavior from reproductive status. Our findings are consistent with a model in which PGF2α communicates fertility status via Ptgfr to circuits in the brain that drive female sexual behavior. Our targeted genome modification in a cichlid fish shows that dissection of gene function can reveal basic control mechanisms for behaviors in this large family of species with diverse and fascinating social systems [16, 17].

    View details for DOI 10.1016/j.cub.2016.01.067

    View details for PubMedID 26996507

  • Two types of dominant male cichlid fish: behavioral and hormonal characteristics. Biology open Alcazar, R. M., Becker, L., Hilliard, A. T., Kent, K. R., Fernald, R. D. 2016; 5 (8): 1061-1071


    Male African cichlid fish, Astatotilapia burtoni, have been classified as dominant or subordinate, each with unique behavioral and endocrine profiles. Here we characterize two distinct subclasses of dominant males based on types of aggressive behavior: (1) males that display escalating levels of aggression and court females while they establish a territory, and (2) males that display a stable level of aggression and delay courting females until they have established a territory. To profile differences in their approach to a challenge, we used an intruder assay. In every case, there was a male-male confrontation between the resident dominant male and the intruder, with the intruder quickly taking a subordinate role. However, we found that dominant males with escalating aggression spent measurably more time attacking subordinates than did dominant males with stable aggression that instead increased their attention toward the females in their tank. There was no difference in the behavior of intruders exposed to either type of dominant male, suggesting that escalating aggression is an intrinsic characteristic of some dominant males and is not elicited by the behavior of their challengers. Male behavior during the first 15 min of establishing a territory predicts their aggressive class. These two types of dominant males also showed distinctive physiological characteristics. After the intruder assay, males with escalating aggression had elevated levels of 11-ketotestosterone (11-KT), testosterone, estradiol, and cortisol, while those with stable aggression did not. These observations show that the same stimulus can elicit different behavioral and endocrine responses among A. burtoni dominant males that characterize them as either escalating or stable aggressive types. Our ability to identify which individuals within a population have escalating levels of aggressive responses versus those which have stable levels of aggressive responses when exposed to the same stimulus, offers a potentially powerful model for investigating the underlying molecular mechanisms that modulate aggressive behavior.

    View details for DOI 10.1242/bio.017640

    View details for PubMedID 27432479

  • Identification of prohormones and pituitary neuropeptides in the African cichlid, Astatotilapia burtoni. BMC genomics Hu, C. K., Southey, B. R., Romanova, E. V., Maruska, K. P., Sweedler, J. V., Fernald, R. D. 2016; 17 (1): 660-?


    Cichlid fishes have evolved remarkably diverse reproductive, social, and feeding behaviors. Cell-to-cell signaling molecules, notably neuropeptides and peptide hormones, are known to regulate these behaviors across vertebrates. This class of signaling molecules derives from prohormone genes that have undergone multiple duplications and losses in fishes. Whether and how subfunctionalization, neofunctionalization, or losses of neuropeptides and peptide hormones have contributed to fish behavioral diversity is largely unknown. Information on fish prohormones has been limited and is complicated by the whole genome duplication of the teleost ancestor. We combined bioinformatics, mass spectrometry-enabled peptidomics, and molecular techniques to identify the suite of neuropeptide prohormones and pituitary peptide products in Astatotilapia burtoni, a well-studied member of the diverse African cichlid clade.Utilizing the A. burtoni genome, we identified 148 prohormone genes, with 21 identified as a single copy and 39 with at least 2 duplicated copies. Retention of prohormone duplicates was therefore 41 %, which is markedly above previous reports for the genome-wide average in teleosts. Beyond the expected whole genome duplication, differences between cichlids and mammals can be attributed to gene loss in tetrapods and additional duplication after divergence. Mass spectrometric analysis of the pituitary identified 620 unique peptide sequences that were matched to 120 unique proteins. Finally, we used in situ hybridization to localize the expression of galanin, a prohormone with exceptional sequence divergence in cichlids, as well as the expression of a proopiomelanocortin, prohormone that has undergone an additional duplication in some bony fish lineages.We characterized the A. burtoni prohormone complement. Two thirds of prohormone families contain duplications either from the teleost whole genome duplication or a more recent duplication. Our bioinformatic and mass spectrometric findings provide information on a major vertebrate clade that will further our understanding of the functional ramifications of these prohormone losses, duplications, and sequence changes across vertebrate evolution. In the context of the cichlid radiation, these findings will also facilitate the exploration of neuropeptide and peptide hormone function in behavioral diversity both within A. burtoni and across cichlid and other fish species.

    View details for DOI 10.1186/s12864-016-2914-9

    View details for PubMedID 27543050

  • The effect of observers on behavior and the brain during aggressive encounters. Behavioural brain research Desjardins, J. K., Becker, L., Fernald, R. D. 2015; 292: 174-183


    What effect does an audience have on an animal's behavior and where is this influence registered in the brain? To answer these questions, we analyzed male cichlid fish fighting in the presence of audiences of various compositions and measured expression of immediate early genes in the brain as a proxy for neural activity. We hypothesized their behavior would change depending on who was watching them. We measured behavioral responses from both the "watchers" and the "watched" during aggressive encounters and found that males fighting in the presence of an audience were more aggressive than males fighting without an audience. Depending on the nature of the audience, immediate early gene expression in key brain nuclei was differentially influenced. Both when an audience of larger males watched fighting males, and when they were watching larger males fighting, nuclei in the brain considered homologous with mammalian nuclei known to be associated with anxiety showed increased activity. When males were in the presence of any audience or when males saw any other males fighting, nuclei in the brain known to be involved in reproduction and aggression were differentially activated relative to control animals. In all cases, there was a close relationship between patterns of brain gene expression between fighters and observers. This suggests that the network of brain regions known as the social behavior network, common across vertebrates, are activated not only in association with the expression of social behavior but also by the reception of social information.

    View details for DOI 10.1016/j.bbr.2015.06.019

    View details for PubMedID 26097004

  • Social behaviour: can it change the brain? ANIMAL BEHAVIOUR Fernald, R. D. 2015; 103: 259-265
  • Electrical synapses connect a network of gonadotropin releasing hormone neurons in a cichlid fish PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Ma, Y., Juntti, S. A., Hu, C. K., Huguenard, J. R., Fernald, R. D. 2015; 112 (12): 3805-3810


    Initiating and regulating vertebrate reproduction requires pulsatile release of gonadotropin-releasing hormone (GnRH1) from the hypothalamus. Coordinated GnRH1 release, not simply elevated absolute levels, effects the release of pituitary gonadotropins that drive steroid production in the gonads. However, the mechanisms underlying synchronization of GnRH1 neurons are unknown. Control of synchronicity by gap junctions between GnRH1 neurons has been proposed but not previously found. We recorded simultaneously from pairs of transgenically labeled GnRH1 neurons in adult male Astatotilapia burtoni cichlid fish. We report that GnRH1 neurons are strongly and uniformly interconnected by electrical synapses that can drive spiking in connected cells and can be reversibly blocked by meclofenamic acid. Our results suggest that electrical synapses could promote coordinated spike firing in a cellular assemblage of GnRH1 neurons to produce the pulsatile output necessary for activation of the pituitary and reproduction.

    View details for DOI 10.1073/pnas.1421851112

    View details for Web of Science ID 000351477000061

    View details for PubMedID 25775522

  • Communication about social status CURRENT OPINION IN NEUROBIOLOGY Fernald, R. D. 2014; 28: 1-4


    Dominance hierarchies are ubiquitous in social species and serve to organize social systems. Social and sexual status is communicated directly among animals via sensory systems evolved in the particular species. Such signals may be chemical, visual, auditory, postural or a combination of signals. In most species, status is initially established through physical conflict between individuals that leads to ritualized conflict or threats, reducing possibly dangerous results of fighting. Many of the status signals contain other information, as in some bird species that communicate both the size of their group and their individual rank vocally. Recent studies have shown that scent signaling among hyenas of east Africa is unique, being produced by fermentative, odor producing bacteria residing in the scent glands.

    View details for DOI 10.1016/j.conb.2014.04.004

    View details for Web of Science ID 000343363000002

    View details for PubMedID 24793315

  • The genomic substrate for adaptive radiation in African cichlid fish NATURE Brawand, D., Wagner, C. E., Li, Y. I., Malinsky, M., Keller, I., Fan, S., Simakov, O., Ng, A. Y., Lim, Z. W., Bezault, E., Turner-Maier, J., Johnson, J., Alcazar, R., Noh, H. J., Russell, P., Aken, B., Alfoeldi, J., Amemiya, C., Azzouzi, N., Baroiller, J., Barloy-Hubler, F., Berlin, A., Bloomquist, R., Carleton, K. L., Conte, M. A., D'Cotta, H., Eshel, O., Gaffney, L., Galibert, F., Gante, H. F., Gnerre, S., Greuter, L., Guyon, R., Haddad, N. S., Haerty, W., Harris, R. M., Hofmann, H. A., Hourlier, T., Hulata, G., Jaffe, D. B., Lara, M., Lee, A. P., MacCallum, I., Mwaiko, S., Nikaido, M., Nishihara, H., Ozouf-Costaz, C., Penman, D. J., Przybylski, D., Rakotomanga, M., Renn, S. C., Ribeiro, F. J., Ron, M., Salzburger, W., Sanchez-Pulido, L., Santos, M. E., Searle, S., Sharpe, T., Swofford, R., Tan, F. J., Williams, L., Young, S., Yin, S., Okada, N., Kocher, T. D., Miska, E. A., Lander, E. S., Venkatesh, B., Fernald, R. D., Meyer, A., Ponting, C. P., Streelman, J. T., Lindblad-Toh, K., Seehausen, O., Di Palma, F. 2014; 513 (7518): 375-?
  • The genomic substrate for adaptive radiation in African cichlid fish. Nature Brawand, D., Wagner, C. E., Li, Y. I., Malinsky, M., Keller, I., Fan, S., Simakov, O., Ng, A. Y., Lim, Z. W., Bezault, E., Turner-Maier, J., Johnson, J., Alcazar, R., Noh, H. J., Russell, P., Aken, B., Alföldi, J., Amemiya, C., Azzouzi, N., Baroiller, J., Barloy-Hubler, F., Berlin, A., Bloomquist, R., Carleton, K. L., Conte, M. A., D'Cotta, H., Eshel, O., Gaffney, L., Galibert, F., Gante, H. F., Gnerre, S., Greuter, L., Guyon, R., Haddad, N. S., Haerty, W., Harris, R. M., Hofmann, H. A., Hourlier, T., Hulata, G., Jaffe, D. B., Lara, M., Lee, A. P., MacCallum, I., Mwaiko, S., Nikaido, M., Nishihara, H., Ozouf-Costaz, C., Penman, D. J., Przybylski, D., Rakotomanga, M., Renn, S. C., Ribeiro, F. J., Ron, M., Salzburger, W., Sanchez-Pulido, L., Santos, M. E., Searle, S., Sharpe, T., Swofford, R., Tan, F. J., Williams, L., Young, S., Yin, S., Okada, N., Kocher, T. D., Miska, E. A., Lander, E. S., Venkatesh, B., Fernald, R. D., Meyer, A., Ponting, C. P., Streelman, J. T., Lindblad-Toh, K., Seehausen, O., Di Palma, F. 2014; 513 (7518): 375-381


    Cichlid fishes are famous for large, diverse and replicated adaptive radiations in the Great Lakes of East Africa. To understand the molecular mechanisms underlying cichlid phenotypic diversity, we sequenced the genomes and transcriptomes of five lineages of African cichlids: the Nile tilapia (Oreochromis niloticus), an ancestral lineage with low diversity; and four members of the East African lineage: Neolamprologus brichardi/pulcher (older radiation, Lake Tanganyika), Metriaclima zebra (recent radiation, Lake Malawi), Pundamilia nyererei (very recent radiation, Lake Victoria), and Astatotilapia burtoni (riverine species around Lake Tanganyika). We found an excess of gene duplications in the East African lineage compared to tilapia and other teleosts, an abundance of non-coding element divergence, accelerated coding sequence evolution, expression divergence associated with transposable element insertions, and regulation by novel microRNAs. In addition, we analysed sequence data from sixty individuals representing six closely related species from Lake Victoria, and show genome-wide diversifying selection on coding and regulatory variants, some of which were recruited from ancient polymorphisms. We conclude that a number of molecular mechanisms shaped East African cichlid genomes, and that amassing of standing variation during periods of relaxed purifying selection may have been important in facilitating subsequent evolutionary diversification.

    View details for DOI 10.1038/nature13726

    View details for PubMedID 25186727

  • Social regulation of cortisol receptor gene expression. journal of experimental biology Korzan, W. J., Grone, B. P., Fernald, R. D. 2014; 217: 3221-3228


    In many social species, individuals influence the reproductive capacity of conspecifics. In a well-studied African cichlid fish species, Astatotilapia burtoni, males are either dominant (D) and reproductively competent or non-dominant (ND) and reproductively suppressed as evidenced by reduced gonadotropin releasing hormone (GnRH1) release, regressed gonads, lower levels of androgens and elevated levels of cortisol. Here, we asked whether androgen and cortisol levels might regulate this reproductive suppression. Astatotilapia burtoni has four glucocorticoid receptors (GR1a, GR1b, GR2 and MR), encoded by three genes, and two androgen receptors (ARα and ARβ), encoded by two genes. We previously showed that ARα and ARβ are expressed in GnRH1 neurons in the preoptic area (POA), which regulates reproduction, and that the mRNA levels of these receptors are regulated by social status. Here, we show that GR1, GR2 and MR mRNAs are also expressed in GnRH1 neurons in the POA, revealing potential mechanisms for both androgens and cortisol to influence reproductive capacity. We measured AR, MR and GR mRNA expression levels in a microdissected region of the POA containing GnRH1 neurons, comparing D and ND males. Using quantitative PCR (qPCR), we found D males had higher mRNA levels of ARα, MR, total GR1a and GR2 in the POA compared with ND males. In contrast, ND males had significantly higher levels of GR1b mRNA, a receptor subtype with a reduced transcriptional response to cortisol. Through this novel regulation of receptor type, neurons in the POA of an ND male will be less affected by the higher levels of cortisol typical of low status, suggesting GR receptor type change as a potential adaptive mechanism to mediate high cortisol levels during social suppression.

    View details for DOI 10.1242/jeb.104430

    View details for PubMedID 25013108

  • Social regulation of cortisol receptor gene expression JOURNAL OF EXPERIMENTAL BIOLOGY Korzan, W. J., Grone, B. P., Fernald, R. D. 2014; 217 (18): 3221-3228

    View details for DOI 10.1242/jeb.104430

    View details for Web of Science ID 000342506100012

  • Social status differences regulate the serotonergic system of a cichlid fish, Astatotilapia burtoni JOURNAL OF EXPERIMENTAL BIOLOGY Loveland, J. L., Uy, N., Maruska, K. P., Carpenter, R. E., Fernald, R. D. 2014; 217 (15): 2680-2690


    Serotonin (5-HT) inhibits aggression and modulates aspects of sexual behaviour in many species, but the mechanisms responsible are not well understood. Here, we exploited the social dominance hierarchy of Astatotilapia burtoni to understand the role of the serotonergic system in long-term maintenance of social status. We identified three populations of 5-HT cells in dorsal and ventral periventricular pretectal nuclei (PPd, PPv), the nucleus of the paraventricular organ (PVO) and raphe. Dominant males had more 5-HT cells than subordinates in the raphe, but the size of these cells did not differ between social groups. Subordinates had higher serotonergic turnover in the raphe and preoptic area (POA), a nucleus essential for hypothalamic-pituitary-gonadal (HPG) axis function. The relative abundance of mRNAs for 5-HT receptor (5-HTR) subtypes 1A and 2A (htr1a, htr2a) was higher in subordinates, a difference restricted to the telencephalon. Because social status is tightly linked to reproductive capacity, we asked whether serotonin turnover and the expression of its receptors correlated with testes size and circulating levels of 11-ketotestosterone (11-KT). We found negative correlations between both raphe and POA serotonin turnover and testes size, as well as between htr1a mRNA levels and circulating 11-KT. Thus, increased serotonin turnover in non-aggressive males is restricted to specific brain nuclei and is associated with increased expression of 5-HTR subtypes 1A and 2A exclusively in the telencephalon.

    View details for DOI 10.1242/jeb.100685

    View details for Web of Science ID 000341189200016

  • Social Opportunity Rapidly Regulates Expression of CRF and CRF Receptors in the Brain during Social Ascent of a Teleost Fish, Astatotilapia burtoni PLOS ONE Carpenter, R. E., Maruska, K. P., Becker, L., Fernald, R. D. 2014; 9 (5)
  • Brains over brawn: experience overcomes a size disadvantage in fish social hierarchies JOURNAL OF EXPERIMENTAL BIOLOGY Alcazar, R. M., Hilliard, A. T., Becker, L., Bernaba, M., Fernald, R. D. 2014; 217 (9): 1462-1468


    Life experiences can alter cognitive abilities and subsequent behavior. Here we asked whether differences in experience could affect social status. In hierarchical animal societies, high-ranking males that typically win aggressive encounters gain territories and hence access to mates. To understand the relative contributions of social experience and physical environment on status, we used a highly territorial African cichlid fish species, Astatotilapia burtoni, that lives in a dynamic lek-like social hierarchy. Astatotilapia burtoni males are either dominant or submissive and can switch status rapidly depending on the local environment. Although dominant males are innately aggressive, we wondered whether they modulated their aggression based on experience. We hypothesized that as males mature they might hone their fighting tactics based on observation of other males fighting. We compared males of different ages and sizes in distinctly different physical environments and subsequently tested their fighting skills. We found that a size difference previously thought negligible (<10% body length) gave a significant advantage to the larger opponent. In contrast, we found no evidence that increasing environmental complexity affected status outcomes. Surprisingly, we found that males only a few days older than their opponents had a significant advantage during territorial disputes so that being older compensated for the disadvantage of being smaller. Moreover, the slightly older winners exploited a consistent fighting strategy, starting with lower levels of aggression on the first day that significantly increased on the second day, a pattern absent in younger winners. These data suggest that experience is an advantage during fights for status, and that social learning provides more relevant experience than the physical complexity of the territory.

    View details for DOI 10.1242/jeb.097527

    View details for Web of Science ID 000335583500014

  • Social opportunity rapidly regulates expression of CRF and CRF receptors in the brain during social ascent of a teleost fish, Astatotilapia burtoni. PloS one Carpenter, R. E., Maruska, K. P., Becker, L., Fernald, R. D. 2014; 9 (5)


    In social animals, hierarchical rank governs food availability, territorial rights and breeding access. Rank order can change rapidly and typically depends on dynamic aggressive interactions. Since the neuromodulator corticotrophin releasing factor (CRF) integrates internal and external cues to regulate the hypothalamic-pituitary adrenal (HPA) axis, we analyzed the CRF system during social encounters related to status. We used a particularly suitable animal model, African cichlid fish, Astatotilapia burtoni, whose social status regulates reproduction. When presented with an opportunity to rise in rank, subordinate A. burtoni males rapidly change coloration, behavior, and their physiology to support a new role as dominant, reproductively active fish. Although changes in gonadotropin-releasing hormone (GnRH1), the key reproductive molecular actor, have been analyzed during social ascent, little is known about the roles of CRF and the HPA axis during transitions. Experimentally enabling males to ascend in social rank, we measured changes in plasma cortisol and the CRF system in specific brain regions 15 minutes after onset of social ascent. Plasma cortisol levels in ascending fish were lower than subordinate conspecifics, but similar to levels in dominant animals. In the preoptic area (POA), where GnRH1 cells are located, and in the pituitary gland, CRF and CRF1 receptor mRNA levels are rapidly down regulated in ascending males compared to subordinates. In the Vc/Vl, a forebrain region where CRF cell bodies are located, mRNA coding for both CRFR1 and CRFR2 receptors is lower in ascending fish compared to stable subordinate conspecifics. The rapid time course of these changes (within minutes) suggests that the CRF system is involved in the physiological changes associated with shifts in social status. Since CRF typically has inhibitory effects on the neuroendocrine reproductive axis in vertebrates, this attenuation of CRF activity may allow rapid activation of the reproductive axis and facilitate the transition to dominance.

    View details for DOI 10.1371/journal.pone.0096632

    View details for PubMedID 24824619

  • Social Regulation of Male Reproductive Plasticity in an African Cichlid Fish INTEGRATIVE AND COMPARATIVE BIOLOGY Maruska, K. P., Fernald, R. D. 2013; 53 (6): 938-950


    Social interactions with the outcome of a position in a dominance hierarchy can have profound effects on reproductive behavior and physiology, requiring animals to integrate environmental information with their internal physiological state; but how is salient information from the animal's dynamic social environment transformed into adaptive behavioral, physiological, and molecular-level changes? The African cichlid fish, Astatotilapia burtoni, is ideally suited to understand socially controlled reproductive plasticity because activity of the male reproductive (brain-pituitary-gonad) axis is tightly linked to social status. Males form hierarchies in which a small percentage of brightly colored dominant individuals have an active reproductive axis, defend territories, and spawn with females, while the remaining males are subordinate, drably colored, do not hold a territory, and have a suppressed reproductive system with minimal opportunities for spawning. These social phenotypes are plastic and quickly reversible, meaning that individual males may switch between dominant and subordinate status multiple times within a lifetime. Here, we review the rapid and remarkable plasticity that occurs along the entire reproductive axis when males rise in social rank, a transition that has important implications for the operational sex ratio of the population. When males rise in rank, transformations occur in the brain, pituitary, circulation, and testes over short time-scales (minutes to days). Changes are evident in overt behavior, as well as modifications at the physiological, cellular, and molecular levels that regulate reproductive capacity. Widespread changes triggered by a switch in rank highlight the significance of external social information in shaping internal physiology and reproductive competence.

    View details for DOI 10.1093/icb/ict017

    View details for Web of Science ID 000327543300007

    View details for PubMedID 23613320

  • Tol2-Mediated Generation of a Transgenic Haplochromine Cichlid, Astatotilapia burtoni PLOS ONE Juntti, S. A., Hu, C. K., Fernald, R. D. 2013; 8 (10)
  • Social descent with territory loss causes rapid behavioral, endocrine and transcriptional changes in the brain JOURNAL OF EXPERIMENTAL BIOLOGY Maruska, K. P., Becker, L., Neboori, A., Fernald, R. D. 2013; 216 (19): 3656-3666


    In social species that form hierarchies where only dominant males reproduce, lower-ranking individuals may challenge higher-ranking ones, often resulting in changes in relative social status. How does a losing animal respond to loss of status? Here, using the African cichlid fish Astatotilapia burtoni, we manipulated the social environment, causing males to descend in rank, and then examined changes in behavior, circulating steroids and immediate early gene (IEG) expression (cfos, egr-1) in micro-dissected brain regions as a proxy for neuronal activation. In particular, we examined changes in the conserved 'social behavior network' (SBN), a collection of brain nuclei known to regulate social behaviors across vertebrates. Astatotilapia burtoni has rapidly reversible dominant-subordinate male phenotypes, so that within minutes, descending males lost their bright body coloration, switched to submissive behaviors and expressed higher plasma cortisol levels compared with non-descending and control males. Descending males had higher IEG expression throughout the SBN, but each brain region showed a distinct IEG-specific response in either cfos or egr-1 levels, but not both. Overall, SBN IEG patterns in descending males were distinctly different from the pattern observed in males ascending (subordinate to dominant) in social status. These results reveal that the SBN rapidly coordinates the perception of social cues about status that are of opposite valence, and translates them into appropriate phenotypic changes. This shows for the first time in a non-mammalian vertebrate that dropping in social rank rapidly activates specific socially relevant brain nuclei in a pattern that differs from when males rise to a higher status position.

    View details for DOI 10.1242/jeb.088617

    View details for Web of Science ID 000324233500019

    View details for PubMedID 23788709

  • Social Opportunity Causes Rapid Transcriptional Changes in the Social Behaviour Network of the Brain in an African Cichlid Fish JOURNAL OF NEUROENDOCRINOLOGY Maruska, K. P., Zhang, A., Neboori, A., Fernald, R. D. 2013; 25 (2): 145-157


    Animals constantly integrate external stimuli with their own internal physiological state to make appropriate behavioural decisions. Little is known, however, about where in the brain the salience of these signals is evaluated, or which neural and transcriptional mechanisms link this integration to adaptive behaviours. We used an African cichlid fish Astatotilapia burtoni to test the hypothesis that a new social opportunity activates the conserved 'social behaviour network' (SBN), a collection of brain nuclei known to regulate social behaviours across vertebrates. We measured mRNA levels of immediate early genes (IEGs) in microdissected brain regions as a proxy for neuronal activation, and discovered that IEGs were higher in all SBN nuclei in males that were given an opportunity to rise in social rank compared to control stable subordinate and dominant individuals. Furthermore, because the presence of sex-steroid receptors is one defining criteria of SBN nuclei, we also tested whether social opportunity or status influenced androgen and oestrogen receptor mRNA levels within these same regions. There were several rapid region-specific changes in receptor mRNA levels induced by social opportunity, most notably in oestrogen receptor subtypes in areas that regulate social aggression and reproduction, suggesting that oestrogenic signalling pathways play an important role in regulating male status. Several receptor mRNA changes occurred in regions with putative homologies to the mammalian septum and extended amygdala, two regions shared by SBN and reward circuits, suggesting an important role in the integration of social salience, stressors, hormonal state and adaptive behaviours. We also demonstrated increases in plasma sex- and stress-steroids at 30 min after a rise in social rank. This rapid endocrine and transcriptional response suggests that the SBN is involved in the integration of social inputs with internal hormonal state to facilitate the transition to dominant status, which ultimately leads to improved fitness for the previously reproductively-suppressed individual.

    View details for DOI 10.1111/j.1365-2826.2012.02382.x

    View details for Web of Science ID 000314072400005

    View details for PubMedID 22958303

  • Social information changes the brain PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Fernald, R. D., Maruska, K. P. 2012; 109: 17194-17199


    Social animals live in complex physical and social environments requiring them to attend and rapidly respond to social and environmental information by changing their behavior. A key social influence is rank or status, a ubiquitous element in animal societies. Rank typically regulates access to reproduction and other resources, among other consequences for individuals. Because reproduction is arguably the most important event in any animals' life, understanding how reproduction is regulated by social status and related physiological factors can instruct our understanding of evolutionary change. This article reviews evidence from a model social system in which reproduction is tightly controlled by social status. Surprisingly, changes in social status have rapid and profound effects over very short time scales and radically alter overt behavior, as well as physiological, cellular, and molecular factors that regulate reproductive capacity.

    View details for DOI 10.1073/pnas.1202552109

    View details for Web of Science ID 000310510500009

    View details for PubMedID 23045669

  • Characterization of cell proliferation throughout the brain of the African cichlid fish Astatotilapia burtoni and its regulation by social status JOURNAL OF COMPARATIVE NEUROLOGY Maruska, K. P., Carpenter, R. E., Fernald, R. D. 2012; 520 (15): 3471-3491


    New cells are added in the brains of all adult vertebrates, but fishes have some of the greatest potential for neurogenesis and gliogenesis among all taxa, partly due to their indeterminate growth. Little is known, however, about how social interactions influence cell proliferation in the brain of these fishes that comprise the largest group of vertebrates. We used 5-bromo-2'-deoxyuridine (BrdU) to identify and localize proliferation zones in the telencephalon, diencephalon, mesencephalon, and rhombencephalon that were primarily associated with ventricular surfaces in the brain of the African cichlid fish Astatotilapia burtoni. Cell migration was evident in some regions by 1 day post injection, and many newborn cells coexpressed the neuronal marker HuC/D at 30 days, suggesting they had differentiated into neurons. To test the hypothesis that social status and perception of an opportunity to rise in rank influenced cell proliferation, we compared numbers of BrdU-labeled cells in multiple brain nuclei among fish of different social status. Socially suppressed subordinate males had the lowest numbers of proliferating cells in all brain regions examined, but males that were given an opportunity to rise in status had higher cell proliferation rates within 1 day, suggesting rapid upregulation of brain mitotic activity associated with this social transition. Furthermore, socially isolated dominant males had similar numbers of BrdU-labeled cells compared with dominant males that were housed in a socially rich environment, suggesting that isolation has little effect on proliferation and that reduced proliferation in subordinates is a result of the social subordination. These results suggest that A. burtoni will be a useful model to analyze the mechanisms of socially induced neurogenesis in vertebrates.

    View details for DOI 10.1002/cne.23100

    View details for Web of Science ID 000307849400009

    View details for PubMedID 22431175

  • Social Context Influences Aggressive and Courtship Behavior in a Cichlid Fish PLOS ONE Desjardins, J. K., Hofmann, H. A., Fernald, R. D. 2012; 7 (7)


    Social interactions require knowledge of the environment and status of others, which can be acquired indirectly by observing the behavior of others. When being observed, animals can also alter their signals based on who is watching. Here we observed how male cichlid fish (Astatotilapia burtoni) behave when being watched in two different contexts. In the first, we show that aggressive and courtship behaviors displayed by subordinate males depends critically on whether dominant males can see them, and in the second, we manipulated who was watching aggressive interactions and showed that dominant males will change their behavior depending on audience composition. In both cases, when a more dominant individual is out of view and the audience consists of more subordinate individuals, those males signal key social information to females by displaying courtship and dominant behaviors. In contrast, when a dominant male is present, males cease both aggression and courtship. These data suggest that males are keenly aware of their social environment and modulate their aggressive and courtship behaviors strategically for reproductive and social advantage.

    View details for DOI 10.1371/journal.pone.0032781

    View details for Web of Science ID 000306366400001

    View details for PubMedID 22807996

  • Food deprivation explains effects of mouthbrooding on ovaries and steroid hormones, but not brain neuropeptide and receptor mRNAs, in an African cichlid fish HORMONES AND BEHAVIOR Grone, B. P., Carpenter, R. E., Lee, M., Maruska, K. P., Fernald, R. D. 2012; 62 (1): 18-26


    Feeding behavior and reproduction are coordinately regulated by the brain via neurotransmitters, circulating hormones, and neuropeptides. Reduced feeding allows animals to engage in other behaviors important for fitness, including mating and parental care. Some fishes cease feeding for weeks at a time in order to provide care to their young by brooding them inside the male or female parent's mouth. Maternal mouthbrooding is known to impact circulating hormones and subsequent reproductive cycles, but neither the full effects of food deprivation nor the neural mechanisms are known. Here we ask what effects mouthbrooding has on several physiological processes including gonad and body mass, brain neuropeptide and receptor gene expression, and circulating steroid hormones in a mouthbrooding cichlid species, Astatotilapia burtoni. We ask whether any observed changes can be explained by food deprivation, and show that during mouthbrooding, ovary size and circulating levels of androgens and estrogens match those seen during food deprivation. Levels of gonadotropin-releasing hormone 1 (GnRH1) mRNA in the brain were low in food-deprived females compared to controls and in mouthbrooding females compared to gravid females. Levels of mRNA encoding two peptides involved in regulating feeding, hypocretin and cholecystokinin, were increased in the brains of food-deprived females. Brain mRNA levels of two receptors, GnRH receptor 2 and NPY receptor Y8c, were elevated in mouthbrooding females compared to the fed condition, but NPY receptor Y8b mRNA was differently regulated by mouthbrooding. These results suggest that many, but not all, of the characteristic physiological changes that occur during mouthbrooding are consequences of food deprivation.

    View details for DOI 10.1016/j.yhbeh.2012.04.012

    View details for Web of Science ID 000305818500003

    View details for PubMedID 22561338

  • The African Cichlid Fish Astatotilapia burtoni Uses Acoustic Communication for Reproduction: Sound Production, Hearing, and Behavioral Significance PLOS ONE Maruska, K. P., Ung, U. S., Fernald, R. D. 2012; 7 (5)


    Sexual reproduction in all animals depends on effective communication between signalers and receivers. Many fish species, especially the African cichlids, are well known for their bright coloration and the importance of visual signaling during courtship and mate choice, but little is known about what role acoustic communication plays during mating and how it contributes to sexual selection in this phenotypically diverse group of vertebrates. Here we examined acoustic communication during reproduction in the social cichlid fish, Astatotilapia burtoni. We characterized the sounds and associated behaviors produced by dominant males during courtship, tested for differences in hearing ability associated with female reproductive state and male social status, and then tested the hypothesis that female mate preference is influenced by male sound production. We show that dominant males produce intentional courtship sounds in close proximity to females, and that sounds are spectrally similar to their hearing abilities. Females were 2-5-fold more sensitive to low frequency sounds in the spectral range of male courtship sounds when they were sexually-receptive compared to during the mouthbrooding parental phase. Hearing thresholds were also negatively correlated with circulating sex-steroid levels in females but positively correlated in males, suggesting a potential role for steroids in reproductive-state auditory plasticity. Behavioral experiments showed that receptive females preferred to affiliate with males that were associated with playback of courtship sounds compared to noise controls, indicating that acoustic information is likely important for female mate choice. These data show for the first time in a Tanganyikan cichlid that acoustic communication is important during reproduction as part of a multimodal signaling repertoire, and that perception of auditory information changes depending on the animal's internal physiological state. Our results highlight the importance of examining non-visual sensory modalities as potential substrates for sexual selection contributing to the incredible phenotypic diversity of African cichlid fishes.

    View details for DOI 10.1371/journal.pone.0037612

    View details for Web of Science ID 000305343500144

    View details for PubMedID 22624055

  • Subordinate male cichlids retain reproductive competence during social suppression PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Kustan, J. M., Maruska, K. P., Fernald, R. D. 2012; 279 (1728): 434-443


    Subordinate males, which are excluded from reproduction often save energy by reducing their investment in sperm production. However, if their position in a dominance hierarchy changes suddenly they should also rapidly attain fertilization capability. Here, we asked how social suppression and ascension to dominance influences sperm quality, spermatogenesis and reproductive competence in the cichlid Astatotilapia burtoni, where reproduction is tightly coupled to social status. Dominant territorial (T) males are reproductively active while subordinate non-territorial (NT) males are suppressed, but given the opportunity, NT males will perform dominance behaviours within minutes and attain T male testes size within days. Using the thymidine analogue 5-bromo-2-deoxyuridine (BrdU) to label germ cell proliferation, we found that the spermatogenic cycle takes approximately 11-12 days, and social status had no effect on proliferation, suggesting that spermatogenesis continues during reproductive suppression. Although sperm velocity did not differ among social states, NT males had reduced sperm motility. Remarkably, males ascending in status showed sperm motility equivalent to T males within 24 h. Males also successfully reproduced within hours of social opportunity, despite four to five weeks of suppression and reduced testis size. Our data suggest that NT males maintain reproductive potential during suppression possibly as a strategy to rapidly improve reproductive fitness upon social opportunity.

    View details for DOI 10.1098/rspb.2011.0997

    View details for Web of Science ID 000298661700003

    View details for PubMedID 21733892

  • Social Control of the Brain ANNUAL REVIEW OF NEUROSCIENCE, VOL 35 Fernald, R. D. 2012; 35: 133-151


    In the course of evolution, social behavior has been a strikingly potent selective force in shaping brains to control action. Physiological, cellular, and molecular processes reflect this evolutionary force, particularly in the regulation of reproductive behavior and its neural circuitry. Typically, experimental analysis is directed at how the brain controls behavior, but the brain is also changed by behavior over evolution, during development, and through its ongoing function. Understanding how the brain is influenced by behavior offers unusual experimental challenges. General principles governing the social regulation of the brain are most evident in the control of reproductive behavior. This is most likely because reproduction is arguably the most important event in an animal's life and has been a powerful and essential selective force over evolution. Here I describe the mechanisms through which behavior changes the brain in the service of reproduction using a teleost fish model system.

    View details for DOI 10.1146/annurev-neuro-062111-150520

    View details for Web of Science ID 000307960400008

    View details for PubMedID 22524786

  • Contextual chemosensory urine signaling in an African cichlid fish JOURNAL OF EXPERIMENTAL BIOLOGY Maruska, K. P., Fernald, R. D. 2012; 215 (1): 68-74


    Chemosensory signaling is crucial for communication in many fish species, but little is known about how signalers modulate chemical output in response to sensory information and social context. Here, we tested the hypothesis that dominant male African cichlid fish (Astatotilapia burtoni) use urine signals during social interactions, and demonstrate that this signaling depends on social context (reproductive; territorial) and on available sensory information (visual cues; full interaction). We injected males with dye to visualize urine pulses and exposed them to full sensory information or visual cues alone of four types: (1) dominant male; (2) gravid (reproductively receptive) females; (3) mouth-brooding (non-receptive) females; or (4) control (no fish). We found that males released urine sooner and increased their urination frequency when visually exposed to gravid females as compared with mouth-brooding females and or no-fish controls. While males could distinguish female reproductive states using visual cues alone, courtship behavior rates were ?10-fold higher when they fully interacted with gravid females compared with receiving visual cues alone. Males also increased their urination and territorial behaviors when exposed to another male, suggesting that chemical signals may convey information on dominance status. These data support the hypothesis that dominant males use urine as a chemical signal and adjust the frequency of their urine output based on contextual information.

    View details for DOI 10.1242/jeb.062794

    View details for Web of Science ID 000298346700015

    View details for PubMedID 22162854

  • Social Regulation of Gene Expression in the Hypothalamic-Pituitary-Gonadal Axis PHYSIOLOGY Maruska, K. P., Fernald, R. D. 2011; 26 (6): 412-423


    Reproduction is a critically important event in every animals' life and in all vertebrates is controlled by the brain via the hypothalamic-pituitary-gonadal (HPG) axis. In many species, this axis, and hence reproductive fitness, can be profoundly influenced by the social environment. Here, we review how the reception of information in a social context causes genomic changes at each level of the HPG axis.

    View details for DOI 10.1152/physiol.00032.2011

    View details for Web of Science ID 000298377300004

    View details for PubMedID 22170959

  • Systems biology meets behavior PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Fernald, R. D. 2011; 108 (44): 17861-17862

    View details for DOI 10.1073/pnas.1115182108

    View details for Web of Science ID 000296373400008

    View details for PubMedID 22025689

  • Animal Cooperation: Keeping a Clean(ing) Reputation CURRENT BIOLOGY Fernald, R. D. 2011; 21 (13): R508-R510


    Cleaner wrasses are a model for the study of animal cooperation. Prospective clients can observe whether the cleaner works faithfully, and cleaners being watched remove just parasites while those that are not, nip the client for a tastier snack.

    View details for DOI 10.1016/j.cub.2011.05.038

    View details for Web of Science ID 000292805400012

    View details for PubMedID 21741588

  • Visual Information Alone Changes Behavior and Physiology during Social Interactions in a Cichlid Fish (Astatotilapia burtoni) PLOS ONE Chen, C., Fernald, R. D. 2011; 6 (5)


    Social behavior can influence physiological systems dramatically yet the sensory cues responsible are not well understood. Behavior of male African cichlid fish, Astatotilapia burtoni, in their natural habitat suggests that visual cues from conspecifics contribute significantly to regulation of social behavior. Using a novel paradigm, we asked whether visual cues alone from a larger conspecific male could influence behavior, reproductive physiology and the physiological stress response of a smaller male. Here we show that just seeing a larger, threatening male through a clear barrier can suppress dominant behavior of a smaller male for up to 7 days. Smaller dominant males being "attacked" visually by larger dominant males through a clear barrier also showed physiological changes for up to 3 days, including up-regulation of reproductive- and stress-related gene expression levels and lowered plasma 11-ketotestesterone concentrations as compared to control animals. The smaller males modified their appearance to match that of non-dominant males when exposed to a larger male but they maintained a physiological phenotype similar to that of a dominant male. After 7 days, reproductive- and stress- related gene expression, circulating hormone levels, and gonad size in the smaller males showed no difference from the control group suggesting that the smaller male habituated to the visual intruder. However, the smaller male continued to display subordinate behaviors and assumed the appearance of a subordinate male for a full week despite his dominant male physiology. These data suggest that seeing a larger male alone can regulate the behavior of a smaller male but that ongoing reproductive inhibition depends on additional sensory cues. Perhaps, while experiencing visual social stressors, the smaller male uses an opportunistic strategy, acting like a subordinate male while maintaining the physiology of a dominant male.

    View details for DOI 10.1371/journal.pone.0020313

    View details for Web of Science ID 000291006500054

    View details for PubMedID 21633515

  • Effects of stress and motivation on performing a spatial task NEUROBIOLOGY OF LEARNING AND MEMORY Wood, L. S., Desjardins, J. K., Fernald, R. D. 2011; 95 (3): 277-285


    Learning is ubiquitous in the animal kingdom but has been studied extensively in only a handful of species. Moreover, learning studied under laboratory conditions is typically unrelated to the animal's natural environment or life history. Here, we designed a task relevant to the natural behavior of male African cichlid fish (Astatotilapia burtoni), to determine if they could be trained on a spatial task to gain access to females and shelter. We measured both how successfully animals completed this task over time and whether and how immediate early gene and hormone expression profiles were related to success. While training fish in a maze, we measured time to task completion, circulating levels of three key hormones (cortisol, 11-ketotestosterone, and testosterone) and mRNA abundance of seven target genes including three immediate early genes (that served proxies for brain activity) in nine brain regions. Data from our subjects fell naturally into three phenotypes: fish that could be trained (learners), fish that could not be trained (non-learners) and fish that never attempted the task (non-attempters). Learners and non-learners had lower levels of circulating cortisol compared to fish that never attempted the task. Learners had the highest immediate early gene mRNA levels in the homologue of the hippocampus (dorsolateral telencephalon; Dl), lower cortisol (stress) levels and were more motivated to accomplish the task as measured by behavioral observations. Fish that never attempted the task showed the lowest activity within the Dl, high stress levels and little to no apparent motivation. Data from non-learners fell between these two extremes in behavior, stress, and motivation.

    View details for DOI 10.1016/j.nlm.2010.12.002

    View details for Web of Science ID 000288774300007

    View details for PubMedID 21145980

  • Acute Light Exposure Suppresses Circadian Rhythms in Clock Gene Expression JOURNAL OF BIOLOGICAL RHYTHMS Grone, B. P., Chang, D., Bourgin, P., Cao, V., Fernald, R. D., Heller, H. C., Ruby, N. F. 2011; 26 (1): 78-81


    Light can induce arrhythmia in circadian systems by several weeks of constant light or by a brief light stimulus given at the transition point of the phase response curve. In the present study, a novel light treatment consisting of phase advance and phase delay photic stimuli given on 2 successive nights was used to induce circadian arrhythmia in the Siberian hamster ( Phodopus sungorus). We therefore investigated whether loss of rhythms in behavior was due to arrhythmia within the suprachiasmatic nucleus (SCN). SCN tissue samples were obtained at 6 time points across 24 h in constant darkness from entrained and arrhythmic hamsters, and per1, per2 , bmal1, and cry1 mRNA were measured by quantitative RT-PCR. The light treatment eliminated circadian expression of clock genes within the SCN, and the overall expression of these genes was reduced by 18% to 40% of entrained values. Arrhythmia in per1, per2, and bmal1 was due to reductions in the amplitudes of their oscillations. We suggest that these data are compatible with an amplitude suppression model in which light induces singularity in the molecular circadian pacemaker.

    View details for DOI 10.1177/0748730410388404

    View details for Web of Science ID 000286424800008

    View details for PubMedID 21252368

  • Plasticity of the Reproductive Axis Caused by Social Status Change in an African Cichlid Fish: I. Pituitary Gonadotropins ENDOCRINOLOGY Maruska, K. P., Levavi-Sivan, B., Biran, J., Fernald, R. D. 2011; 152 (1): 281-290


    Social position in a dominance hierarchy is often tightly coupled with fertility. Consequently, an animal that can recognize and rapidly take advantage of an opportunity to rise in rank will have a reproductive advantage. Reproduction in all vertebrates is controlled by the brain-pituitary-gonad axis, and in males of the African cichlid fish Astatotilapia burtoni, GnRH1 neurons at the apex of this axis are under social control. However, little is known about how quickly social information is transformed into functional reproductive change, or about how socially controlled changes in GnRH1 neurons influence downstream actions of the brain-pituitary-gonad axis. We created an opportunity for reproductively suppressed males to ascend in status and then measured how quickly the perception of this opportunity caused changes in mRNA and protein levels of the pituitary gonadotropins. mRNA levels of the ?-subunits of LH and FSH rose rapidly in the pituitary 30 min after suppressed males perceived an opportunity to ascend. In contrast, mRNA levels of GnRH receptor-1 remained unchanged during social transition but were higher in stable dominant compared with subordinate males. In the circulation, levels of both LH and FSH were also quickly elevated. There was a positive correlation between mRNA in the pituitary and circulating protein levels for LH and FSH, and both gonadotropins were positively correlated with plasma 11-ketotestosterone. Our results show that the pituitary is stimulated extremely rapidly after perception of social opportunity, probably to allow suppressed males to quickly achieve reproductive success in a dynamic social environment.

    View details for DOI 10.1210/en.2010-0875

    View details for Web of Science ID 000285573000029

    View details for PubMedID 21068157

  • Plasticity of the Reproductive Axis Caused by Social Status Change in an African Cichlid Fish: II. Testicular Gene Expression and Spermatogenesis ENDOCRINOLOGY Maruska, K. P., Fernald, R. D. 2011; 152 (1): 291-302


    Reproduction in all vertebrates is controlled by the brain-pituitary-gonad (BPG) axis, which is regulated socially in males of the African cichlid fish Astatotilapia burtoni. Although social information influences GnRH1 neurons at the apex of the BPG axis, little is known about how the social environment and dominance affects the cellular and molecular composition of the testes to regulate reproductive capacity. We created an opportunity for reproductively suppressed males to ascend in status and then measured changes in gene expression and tissue morphology to discover how quickly the perception of this opportunity can influence the testes. Our results show rapid up-regulation of mRNA levels of FSH receptor and several steroid receptor subtypes in the testes during social ascent. In contrast, LH receptor was not elevated until 72 h after ascent, but this increase was coincident with elevated circulating androgens and early stages of spermatogenesis, suggesting a role in steroidogenesis. The spermatogenic potential of the testes, as measured by cellular composition, was also elevated before the overall increase in testes size. The presence of cysts at all stages of spermatogenesis, coupled with lower levels of gonadotropin and steroid receptors in subordinate males, suggests that the BPG axis and spermatogenesis are maintained at a subthreshold level in anticipation of the chance to gain a territory and become reproductively active. Our results show that the testis is stimulated extremely quickly after perception of social opportunity, presumably to allow suppressed males to rapidly achieve high reproductive success in a dynamic social environment.

    View details for DOI 10.1210/en.2010-0876

    View details for Web of Science ID 000285573000030

    View details for PubMedID 21084443

  • What do fish make of mirror images? BIOLOGY LETTERS Desjardins, J. K., Fernald, R. D. 2010; 6 (6): 744-747


    Fish act aggressively towards their mirror image suggesting that they consider it another individual, whereas in some mammals behavioural response to mirrors may be an evidence of self-recognition. Since fish cannot self-recognize, we asked whether they could distinguish between fighting a mirror image and fighting a real fish. We compared molecular, physiological and behavioural responses in each condition and found large differences in brain gene expression levels. Although neither levels of aggressive behaviour nor circulating androgens differed between these conditions, males fighting a mirror image had higher immediate early gene (IEG) expression in brain areas homologous to the amygdala and hippocampus than controls. Since amygdalar responses are associated with fear and fear conditioning in other species, higher levels of brain activation when fighting a mirror suggest fish experience fear in response to fights with a mirror image. Clearly, the fish recognize something unusual about the mirror image and the differential brain response may reflect a cognitive distinction.

    View details for DOI 10.1098/rsbl.2010.0247

    View details for Web of Science ID 000284104000007

    View details for PubMedID 20462889

  • Female genomic response to mate information PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Desjardins, J. K., Klausner, J. Q., Fernald, R. D. 2010; 107 (49): 21176-21180


    Females should be choosier than males about prospective mates because of the high costs of inappropriate mating decisions. Both theoretical and empirical studies have identified factors likely to influence female mate choices. However, male-male social interactions also can affect mating decisions, because information about a potential mate can trigger changes in female reproductive physiology. We asked how social information about a preferred male influenced neural activity in females, using immediate early gene (IEG) expression as a proxy for brain activity. A gravid female cichlid fish (Astatotilapia burtoni) chose between two socially equivalent males and then saw fights between these two males in which her preferred male either won or lost. We measured IEG expression levels in several brain nuclei including those in the vertebrate social behavior network (SBN), a collection of brain nuclei known to be important in social behavior. When the female saw her preferred male win a fight, SBN nuclei associated with reproduction were activated, but when she saw her preferred male lose a fight, the lateral septum, a nucleus associated with anxiety, was activated instead. Thus social information alone, independent of actual social interactions, activates specific brain regions that differ significantly depending on what the female sees. In female brains, reproductive centers are activated when she chooses a winner, and anxiety-like response centers are activated when she chooses a loser. These experiments assessing the role of mate-choice information on the brain using a paradigm of successive presentations of mate information suggest ways to understand the consequences of social information on animals using IEG expression.

    View details for DOI 10.1073/pnas.1010442107

    View details for Web of Science ID 000285050800060

    View details for PubMedID 21106763

  • Neurobiology of behavior CURRENT OPINION IN NEUROBIOLOGY Fernald, R. D., Scharff, C. 2010; 20 (6): 746-747

    View details for DOI 10.1016/j.conb.2010.10.001

    View details for Web of Science ID 000287272800009

    View details for PubMedID 21071204

  • Reproductive status regulates expression of sex steroid and GnRH receptors in the olfactory bulb BEHAVIOURAL BRAIN RESEARCH Maruska, K. P., Fernald, R. D. 2010; 213 (2): 208-217


    Neuromodulators including gonadotropin-releasing hormone (GnRH) and sex steroids help integrate an animal's internal physiological state with incoming external cues, and can have profound effects on the processing of behaviorally relevant information, particularly from the olfactory system. While GnRH and steroid receptors are present in olfactory processing regions across vertebrates, little is known about whether their expression levels change with internal physiological state or external social cues. We used qRT-PCR to measure mRNA levels of two GnRH receptors (GnRH-R1, GnRH-R2), five sex steroid receptors (estrogen receptors: ERalpha, ERbetaa, ERbetab; androgen receptors: ARalpha, ARbeta), and aromatase in the olfactory bulb of the highly social African cichlid fish Astatotilapia burtoni. We asked whether these receptor levels changed with reproductive condition in females, or with social status, which regulates reproductive capacity in males. Our results reveal that mRNA levels of multiple sex steroid, GnRH receptor subtypes, and aromatase in the olfactory bulb vary with sex, social status in males, and reproductive condition in females, which highlights the potential importance of changing receptor levels in fine-tuning the olfactory system during the reproductive cycle. Further, steroid receptor mRNA levels were positively correlated with circulating steroid levels in males, but negatively correlated in females, suggesting different regulatory control between sexes. These results provide support for the hypothesis that the first-order olfactory relay station is a substrate for both GnRH and sex steroid modulation, and suggest that changes in receptor levels could be an important mechanism for regulating reproductive, social, and seasonal plasticity in olfactory perception observed across vertebrates.

    View details for DOI 10.1016/j.bbr.2010.04.058

    View details for Web of Science ID 000279748600011

    View details for PubMedID 20466023

  • Social status regulates kisspeptin receptor mRNA in the brain of Astatotilapia burtoni GENERAL AND COMPARATIVE ENDOCRINOLOGY Grone, B. P., Maruska, K. P., Korzan, W. J., Fernald, R. D. 2010; 169 (1): 98-107


    The brain controls reproduction in response to relevant external and internal cues. Central to this process in vertebrates is gonadotropin-releasing hormone (GnRH1) produced in neurons of the hypothalamic-preoptic area (POA). GnRH1 released from the POA stimulates pituitary release of gonadotropins, which in males causes sperm production and concomitant steroid hormone release from the testes. Kisspeptin, a neuropeptide acting via the kisspeptin receptor (Kiss1r), increases GnRH1 release and is linked to development of the reproductive system in mammals and other vertebrates. In both fish and mammals, kiss1r mRNA levels increase in the brain around the time of puberty but the environmental and other stimuli regulating kisspeptin signaling to GnRH1 neurons remain unknown. To understand where kiss1r is expressed and how it is regulated in the brain of a cichlid fish, Astatotilapia burtoni, we measured expression of a kiss1r homolog mRNA by in situ hybridization and quantitative reverse transcription-PCR (qRT-PCR). We found kiss1r mRNA localized in the olfactory bulb, specific nuclei in the telencephalon, diencephalon, mesencephalon, and rhombencephalon, as well as in GnRH1 and GnRH3 neurons. Since males' sexual physiology and behavior depend on social status in A. burtoni, we also tested how status influenced kiss1r mRNA levels. We found higher kiss1r mRNA levels in whole brains of high status territorial males and lower levels in low status non-territorial males. Our results are consistent with the hypothesis that Kiss1r regulates many functions in the brain, making it a strong candidate for mediating differences in reproductive physiology between territorial and non-territorial phenotypes.

    View details for DOI 10.1016/j.ygcen.2010.07.018

    View details for Web of Science ID 000282260800013

    View details for PubMedID 20688063

  • Behavioral and physiological plasticity: Rapid changes during social ascent in an African cichlid fish HORMONES AND BEHAVIOR Maruska, K. P., Fernald, R. D. 2010; 58 (2): 230-240


    In many vertebrates, reproduction is regulated by social interactions in which dominant males control access to females and food. Subordinate males that displace dominant individuals must rapidly adopt behavioral and physiological traits of the higher rank to gain reproductive success. To understand the process of phenotypic plasticity during social ascent, we analyzed the temporal expression pattern of dominance behaviors and circulating androgen levels when socially-suppressed males of an African cichlid fish Astatotilapia burtoni ascended in status. These experiments tested a prediction of the 'challenge hypothesis' that, during periods of social instability, male androgen levels are higher than during socially stable times. We found that socially and reproductively suppressed males perform territorial and reproductive behaviors within minutes of an opportunity to ascend in status, and that animals switch from initial expression of territorial behaviors to more reproductive behaviors during territory establishment. Following this rapid response, social stability may be achieved within 1-3 days of social ascent. Consistent with predictions of the 'challenge hypothesis', circulating 11-ketotestosterone (11-KT) levels were elevated within 30 min following social opportunity, coincident with increased aggressive behavior. However, territorial behaviors and serum 11-KT levels were then dissociated by 72h after social ascent, suggesting either rapid social stability and/or increased physiological potential for androgen production. This behavioral and physiological plasticity in male A. burtoni suggests that perception of social opportunity triggers a suite of quick changes to facilitate rapid transition towards reproductive success, and reveals important features of social ascent not previously recognized.

    View details for DOI 10.1016/j.yhbeh.2010.03.011

    View details for Web of Science ID 000278981500006

    View details for PubMedID 20303357

  • NPY and GnRH Systems Respond to Food Deprivation in a Mouthbrooding Cichlid Grone, B. P., Lee, M., Fernald, R. D. OXFORD UNIV PRESS INC. 2010: E64-E64
  • Steroid receptor expression in the fish inner ear varies with sex, social status, and reproductive state BMC NEUROSCIENCE Maruska, K. P., Fernald, R. D. 2010; 11


    Gonadal and stress-related steroid hormones are known to influence auditory function across vertebrates but the cellular and molecular mechanisms responsible for steroid-mediated auditory plasticity at the level of the inner ear remain unknown. The presence of steroid receptors in the ear suggests a direct pathway for hormones to act on the peripheral auditory system, but little is known about which receptors are expressed in the ear or whether their expression levels change with internal physiological state or external social cues. We used qRT-PCR to measure mRNA expression levels of multiple steroid receptor subtypes (estrogen receptors: ERalpha, ERbetaa, ERbetab; androgen receptors: ARalpha, ARbeta; corticosteroid receptors: GR2, GR1a/b, MR) and aromatase in the main hearing organ of the inner ear (saccule) in the highly social African cichlid fish Astatotilapia burtoni, and tested whether these receptor levels were correlated with circulating steroid concentrations.We show that multiple steroid receptor subtypes are expressed within the main hearing organ of a single vertebrate species, and that expression levels differ between the sexes. We also show that steroid receptor subtype-specific changes in mRNA expression are associated with reproductive phase in females and social status in males. Sex-steroid receptor mRNA levels were negatively correlated with circulating estradiol and androgens in both males and females, suggesting possible ligand down-regulation of receptors in the inner ear. In contrast, saccular changes in corticosteroid receptor mRNA levels were not related to serum cortisol levels. Circulating steroid levels and receptor subtype mRNA levels were not as tightly correlated in males as compared to females, suggesting different regulatory mechanisms between sexes.This is the most comprehensive study of sex-, social-, and reproductive-related steroid receptor mRNA expression in the peripheral auditory system of any single vertebrate. Our data suggest that changes in steroid receptor mRNA expression in the inner ear could be a regulatory mechanism for physiological state-dependent auditory plasticity across vertebrates.

    View details for DOI 10.1186/1471-2202-11-58

    View details for Web of Science ID 000278230000002

    View details for PubMedID 20433748

  • Regulation of gonadotropin-releasing hormone-1 gene transcription by members of the purine-rich element-binding protein family AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM Zhao, S., Kelm, R. J., Fernald, R. D. 2010; 298 (3): E524-E533


    Gonadotropin-releasing hormone-1 (GnRH1) controls reproduction by stimulating the release of gonadotropins from the pituitary. To characterize regulatory factors governing GnRH1 gene expression, we employed biochemical and bioinformatics techniques to identify novel GnRH1 promoter-binding proteins from the brain of the cichlid fish, Astatotilapia burtoni (A. burtoni). Using an in vitro DNA-binding assay followed by mass spectrometric peptide mapping, we identified two members of the purine-rich element-binding (Pur) protein family, Puralpha and Purbeta, as candidates for GnRH1 promoter binding and regulation. We found that transcripts for both Puralpha and Purbeta colocalize in GnRH1-expressing neurons in the preoptic area of the hypothalamus in A. burtoni brain. Furthermore, we confirmed in vivo binding of endogenous Puralpha and Purbeta to the upstream region of the GnRH1 gene in A. burtoni brain and mouse neuronal GT1-7 cells. Consistent with the relative promoter occupancy exhibited by endogenous Pur proteins, overexpression of Purbeta, but not Puralpha, significantly downregulated GnRH1 mRNA levels in transiently transfected GT1-7 cells, suggesting that Purbeta acts as a repressor of GnRH1 gene transcription.

    View details for DOI 10.1152/ajpendo.00597.2009

    View details for Web of Science ID 000274705200016

    View details for PubMedID 19996387

  • Fish sex: why so diverse? CURRENT OPINION IN NEUROBIOLOGY Desjardins, J. K., Fernald, R. D. 2009; 19 (6): 648-653

    View details for DOI 10.1016/j.conb.2009.09.015

    View details for Web of Science ID 000273864300013

    View details for PubMedID 19906523

  • Gonadotropin-Releasing Hormone Receptors: Where Did They Come From? ENDOCRINOLOGY Fernald, R. D. 2009; 150 (6): 2507-2508

    View details for DOI 10.1210/en.2009-0475

    View details for Web of Science ID 000266256700004

    View details for PubMedID 19458247

  • Cytoarchitecture of a Cichlid Fish Telencephalon BRAIN BEHAVIOR AND EVOLUTION Burmeister, S. S., Munshi, R. G., Fernald, R. D. 2009; 74 (2): 110-120


    Although the telencephalon of ray-finned fishes has garnered considerable attention from comparative neuroanatomists, detailed descriptions of telencephalic organization are available for only a few species. This necessarily limits our understanding of telencephalic evolution, particularly in light of the extraordinary diversity of ray-finned fishes. Thus, we have charted the cyctoarchitecture of the telencephalon of the African cichlid fish, Astatotilapia (Haplochromis) burtoni. We examined tissue sectioned in the transverse plane, and categorized cell groups based on size, shape, and staining intensity of cells, the density and distribution of cells, cell-poor zones, and relationship of cell groups to the anterior commissure and external sulci. In addition, to facilitate visualization of the transitions among cell groups, we aligned and animated a series of 100 sequential brain sections. We found that the A. burtoni telencephalon was similar to other percomorphs in being highly elaborated with many distinct cell groups. In the pallium, Dm, Dl, and Dc had a large number of cell groups, whereas Dd and Dp were more uniform. Although we recognized many similarities between the pallium of A. burtoni and other teleosts, we also recognized two cell groups (Dl-g and Dm-2) that might represent specializations of cichlids. We found that the subpallium had a similar organization to that of other ray-finned fishes.

    View details for DOI 10.1159/000235613

    View details for Web of Science ID 000271425500003

    View details for PubMedID 19729898

  • Genes and Social Behavior SCIENCE Robinson, G. E., Fernald, R. D., Clayton, D. F. 2008; 322 (5903): 896-900


    What genes and regulatory sequences contribute to the organization and functioning of neural circuits and molecular pathways in the brain that support social behavior? How does social experience interact with information in the genome to modulate brain activity? Here, we address these questions by highlighting progress that has been made in identifying and understanding two key "vectors of influence" that link genes, the brain, and social behavior: (i) Social information alters gene expression in the brain to influence behavior, and (ii) genetic variation influences brain function and social behavior. We also discuss how evolutionary changes in genomic elements influence social behavior and outline prospects for a systems biology of social behavior.

    View details for DOI 10.1126/science.1159277

    View details for Web of Science ID 000260674100034

    View details for PubMedID 18988841

  • How do social dominance and social information influence reproduction and the brain ? Desjardins, J. K., Fernald, R. D. OXFORD UNIV PRESS INC. 2008: 596-603


    How does living in a social environment influence the brain? In particular, we ask the following questions: How do animals perceive and use social information? How does the perception of social information influence the reproductive system? Where is this represented in the brain? We present a model system in which these questions can be addressed, focusing on the brain's role in integrating information. In the social fish, Astatotilapia burtoni (Haplochromis), the relationship between social status and gonadotropin-releasing hormone (GnRH1) has been well established. Change in status results in numerous changes in the physiology of A. burtoni at every level of organization. Social status can regulate reproduction via the hypothalamic-pituitary-gonadal (HPG) axis. GnRH1 is used by the brain to signal the pituitary about reproductive state so reproductive control depends on regulation of this signaling peptide. In this fish, social dominance is tightly coupled to fertility. Here, we have exploited this link to understand the regulatory systems from circulating hormones, brain volume to gene expression.

    View details for DOI 10.1093/icb/icn089

    View details for Web of Science ID 000260981000006

    View details for PubMedID 21669819

  • Expression of arginine vasotocin in distinct preoptic regions is associated with dominant and subordinate behaviour in an African cichlid fish PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Greenwood, A. K., Wark, A. R., Fernald, R. D., Hofmann, H. A. 2008; 275 (1649): 2393-2402


    Neuropeptides have widespread modulatory effects on behaviour and physiology and are associated with phenotypic transitions in a variety of animals. Arginine vasotocin (AVT) is implicated in mediating alternative male phenotypes in teleost fish, but the direction of the association differs among species, with either higher or lower AVT related to more territorial behaviour in different fishes. To clarify the complex relationship between AVT and alternative phenotype, we evaluated AVT expression in an African cichlid in which social status is associated with divergent behaviour and physiology. We compared AVT mRNA expression between territorial and non-territorial (NT) males in both whole brains and microdissected anterior preoptic areas using transcription profiling, and in individual preoptic nuclei using in situ hybridization. These complementary methods revealed that in the posterior preoptic area (gigantocellular nucleus), territorial males exhibit higher levels of AVT expression than NT males. Conversely, in the anterior preoptic area (parvocellular nucleus), AVT expression is lower in territorial males than NT males. We further correlated AVT expression with behavioural and physiological characteristics of social status to gain insight into the divergent functions of individual AVT nuclei. Overall, our findings highlight a complex association between AVT and social behaviour.

    View details for DOI 10.1098/rspb.2008.0622

    View details for Web of Science ID 000258970600012

    View details for PubMedID 18628117

  • GnRH and GnRH receptors: distribution, function and evolution JOURNAL OF FISH BIOLOGY Chen, C., Fernald, R. D. 2008; 73 (5): 1099-1120
  • Color change as a potential behavioral strategy HORMONES AND BEHAVIOR Korzan, W. J., Robison, R. R., Zhao, S., Fernald, R. D. 2008; 54 (3): 463-470


    Within species, color morphs may enhance camouflage, improve communication and/or confer reproductive advantage. However, in the male cichlid Astatotilapia burtoni, body color may also signal a behavioral strategy. A. burtoni live in a lek-like social system in Lake Tanganyika, Africa where bright blue or yellow territorial (T) males (together ~10-30% of the population) are reproductively capable and defend territories containing food with a spawning site. In contrast, non-territorial (NT) males are smaller, cryptically colored, shoal with females and have regressed gonads. Importantly, males switch between these social states depending on their success in aggressive encounters. Yellow and blue morphs were thought to be adaptations to particular habitats, but they co-exist both in nature and in the laboratory. Importantly, individual males can switch colors so we asked whether color influences behavioral and hormonal profiles. When pairing territorial males with opposite colored fish, yellow males became dominant over blue males significantly more frequently. Moreover, yellow T males had significantly higher levels of 11-ketotosterone than blue T males while only blue NT males had higher levels of the stress hormone cortisol compared to the other groups. Thus color differences alone predict dominance status and hormone profiles in T males. Since T males can and do change color, this suggests that A. burtoni may use color as a flexible behavioral strategy.

    View details for DOI 10.1016/j.yhbeh.2008.05.006

    View details for Web of Science ID 000258812900017

    View details for PubMedID 18586245

  • Sequences, expression patterns and regulation of the corticotropin-releasing factor system in a teleost GENERAL AND COMPARATIVE ENDOCRINOLOGY Chen, C., Fernald, R. D. 2008; 157 (2): 148-155


    Corticotropin-releasing factor (CRF) is well known for its role in regulating the stress response in vertebrate species by controlling release of glucocorticoids. CRF also influences other physiological processes via two distinct CRF receptors (CRF-Rs) and is co-regulated by a CRF binding protein (CRFBP). Although CRF was first discovered in mammals, it is important for the regulation of the stress response, motor behavior, and appetite in all vertebrates. However, it is unclear how the actions of CRF, CRF-Rs, and CRFBP are coordinated. To approach this problem, we cloned and identified CRF, CRF-Rs, and CRFBP in a teleost fish model system, Astatotilapia burtoni and mapped their expression patterns in the body and brain. We found that CRF, CRFBP, and CRF-Rs gene sequences are highly conserved across vertebrates, suggesting that the CRF system plays an essential role in survival. Members of the CRF system are expressed widely in the brain, retina, gill, spleen, muscle, and kidney, thereby implicating them in a variety of bodily functions, including vision, respiration, digestion, and movement. We also found that following long-term social stress, mRNA expression of CRF in the brain and CRF type 1 receptor in the pituitary decrease whereas CRFBP in the pituitary increases via a homeostatic mechanism.

    View details for DOI 10.1016/j.ygcen.2008.04.003

    View details for Web of Science ID 000257087000008

    View details for PubMedID 18501902

  • Heterogeneous nuclear ribonucleoprotein A/B and G inhibits the transcription of gonadotropin-releasing-hormone 1 MOLECULAR AND CELLULAR NEUROSCIENCE Zhao, S., Korzan, W. J., Chen, C., Femald, R. D. 2008; 37 (1): 69-84


    Gonadotropin-releasing hormone 1 (GnRH1) causes the release of gonadotropins from the pituitary to control reproduction. Here we report that two heterogeneous nuclear ribonucleoproteins (hnRNP-A/B and hnRNP-G) bind to the GnRH-I upstream promoter region in a cichlid fish Astatotilapia burtoni. We identified these binding proteins using a newly developed homology based method of mass spectrometric peptide mapping. We show that both hnRNP-A/B and hnRNP-G co-localize with GnRH1 in the pre-optic area of the hypothalamus in the brain. We also demonstrated that these ribonucleoproteins exhibit similar binding capacity in vivo, using immortalized mouse GT1-7 cells where overexpression of either hnRNP-A/B or hnRNP-G significantly down-regulates GnRH1 mRNA levels in GT1-7 cells, suggesting that both act as repressors in GnRH1 transcriptional regulation.

    View details for DOI 10.1016/j.mcn.2007.08.015

    View details for Web of Science ID 000252683100007

    View details for PubMedID 17920292

  • Localization and diurnal expression of melanopsin, vertebrate ancient opsin, and pituitary adenylate cyclase-activating peptide mRNA in a teleost retina JOURNAL OF BIOLOGICAL RHYTHMS Grone, B. P., Zhao, S., Chen, C., Fernald, R. D. 2007; 22 (6): 558-561

    View details for DOI 10.1177/0748730407308285

    View details for Web of Science ID 000251196700011

    View details for PubMedID 18057331

  • Expression, structure, function, and evolution of gonadotropin-releasing hormone (GnRH) receptors GnRH-R1(SHS) and GnRH-R2(PEY) in the teleost, Astatotilapia burtoni ENDOCRINOLOGY Flanagan, C. A., Chen, C., Coetsee, M., Mamputha, S., Whitlock, K. E., Bredenkamp, N., Grosenick, L., Fernald, R. D., Illing, N. 2007; 148 (10): 5060-5071


    Multiple GnRH receptors are known to exist in nonmammalian species, but it is uncertain which receptor type regulates reproduction via the hypothalamic-pituitary-gonadal axis. The teleost fish, Astatotilapia burtoni, is useful for identifying the GnRH receptor responsible for reproduction, because only territorial males reproduce. We have cloned a second GnRH receptor in A. burtoni, GnRH-R1(SHS) (SHS is a peptide motif in extracellular loop 3), which is up-regulated in pituitaries of territorial males. We have shown that GnRH-R1(SHS) is expressed in many tissues and specifically colocalizes with LH in the pituitary. In A. burtoni brain, mRNA levels of both GnRH-R1(SHS) and a previously identified receptor, GnRH-R2(PEY), are highly correlated with mRNA levels of all three GnRH ligands. Despite its likely role in reproduction, we found that GnRH-R1(SHS) has the highest affinity for GnRH2 in vitro and low responsivity to GnRH1. Our phylogenetic analysis shows that GnRH-R1(SHS) is less closely related to mammalian reproductive GnRH receptors than GnRH-R2(PEY). We correlated vertebrate GnRH receptor amino acid sequences with receptor function and tissue distribution in many species and found that GnRH receptor sequences predict ligand responsiveness but not colocalization with pituitary gonadotropes. Based on sequence analysis, tissue localization, and physiological response we propose that the GnRH-R1(SHS) receptor controls reproduction in teleosts, including A. burtoni. We propose a GnRH receptor classification based on gene sequence that correlates with ligand selectivity but not with reproductive control. Our results suggest that different duplicated GnRH receptor genes have been selected to regulate reproduction in different vertebrate lineages.

    View details for DOI 10.1210/en.2006-1400

    View details for Web of Science ID 000249525600060

    View details for PubMedID 17595228

  • Androgen receptors in a cichlid fish, Astatotilapia burtoni: Structure, localization, and expression levels JOURNAL OF COMPARATIVE NEUROLOGY Harbott, L. K., Burmeister, S. S., White, R. B., Vagell, M., Fernald, R. D. 2007; 504 (1): 57-73


    Androgens are an important output of the hypothalamic-pituitary-gonadal (HPG) axis that controls reproduction in all vertebrates. In male teleosts two androgens, testosterone and 11-ketotestosterone, control sexual differentiation and development in juveniles and reproductive behavior in adults. Androgenic signals provide feedback at many levels of the HPG axis, including the hypothalamic neurons that synthesize and release gonadotropin-releasing hormone 1 (GnRH1), but the precise cellular site of androgen action in the brain is not known. Here we describe two androgen receptor subtypes, ARalpha and ARbeta, in the cichlid Astatotilapia burtoni and show that these subtypes are differentially located throughout the adult brain in nuclei known to function in the control of reproduction. ARalpha was expressed in the ventral part of the ventral telencephalon, the preoptic area (POA) of the hypothalamus and the ventral hypothalamus, whereas ARbeta was more widely expressed in the dorsal and ventral telencephalon, the POA, and the ventral and dorsal hypothalamus. We provide the first evidence in any vertebrate that the GnRH1-releasing neurons, which serve as the central control point of the HPG axis, express both subtypes of AR. Using quantitative real-time PCR, we show that A. burtoni AR subtypes have different expression levels in adult tissue, with ARalpha showing significantly higher expression than ARbeta in the pituitary, and ARbeta expressed at a higher level than ARalpha in the anterior and middle brain. These data provide important insight into the role of androgens in regulating the vertebrate reproductive axis.

    View details for DOI 10.1002/cne.21435

    View details for Web of Science ID 000248419000004

    View details for PubMedID 17614300

  • Territorial male color predicts agonistic behavior of conspecifics in a color polymorphic species BEHAVIORAL ECOLOGY Korzan, W. J., Fernald, R. D. 2007; 18 (2): 318-323
  • Fish can infer social rank by observation alone NATURE Grosenick, L., Clement, T. S., Fernald, R. D. 2007; 445 (7126): 429-432


    Transitive inference (TI) involves using known relationships to deduce unknown ones (for example, using A > B and B > C to infer A > C), and is thus essential to logical reasoning. First described as a developmental milestone in children, TI has since been reported in nonhuman primates, rats and birds. Still, how animals acquire and represent transitive relationships and why such abilities might have evolved remain open problems. Here we show that male fish (Astatotilapia burtoni) can successfully make inferences on a hierarchy implied by pairwise fights between rival males. These fish learned the implied hierarchy vicariously (as 'bystanders'), by watching fights between rivals arranged around them in separate tank units. Our findings show that fish use TI when trained on socially relevant stimuli, and that they can make such inferences by using indirect information alone. Further, these bystanders seem to have both spatial and featural representations related to rival abilities, which they can use to make correct inferences depending on what kind of information is available to them. Beyond extending TI to fish and experimentally demonstrating indirect TI learning in animals, these results indicate that a universal mechanism underlying TI is unlikely. Rather, animals probably use multiple domain-specific representations adapted to different social and ecological pressures that they encounter during the course of their natural lives.

    View details for DOI 10.1038/nature05511

    View details for Web of Science ID 000243689500040

    View details for PubMedID 17251980

  • Social dominance regulates androgen and estrogen receptor gene expression HORMONES AND BEHAVIOR Burmeister, S. S., Kailasanath, V., Fernald, R. D. 2007; 51 (1): 164-170


    In Astatotilapia burtoni, dominant males have higher levels of sex steroid hormones than subordinate males. Because of the complex regulatory interactions between steroid hormones and receptors, we asked whether dominance is also associated with variation in sex steroid receptor gene expression. Using quantitative PCR, we compared the expression of specific subtypes of androgen (AR) and estrogen (ER) receptor genes between dominant and subordinated males in 3 divisions of the brain, the pituitary, and the testes. We measured mRNA levels of AR-alpha, AR-beta, ER-alpha, ER-betaa, and ER-betab, gonadotropin-releasing hormone 1 (GnRH1), and GnRH receptor 1 (GnRH-R1) relative to 18S rRNA. In the anterior part of the brain, we found that dominant males had higher mRNA expression of AR-alpha, AR-beta, ER-betaa, and ER-betab, but not ER-alpha, compared to subordinate males. This effect of dominance was reflected in a positive correlation between testes size and AR-alpha, AR-beta, ER-betaa, and ER-betab in the anterior brain. In addition, mRNA levels of all ARs and ERs in the anterior brain were positively correlated with mRNA level of GnRH1. In the middle and posterior portions of the brain, as well as the testes, steroid receptor mRNA levels were similar among dominants and subordinates. In the pituitary, ER-alpha mRNA level was positively correlated with testes size and AR-alpha mRNA was positively correlated with GnRH-R1 mRNA level. These data suggest that dominant male brains could be more sensitive to sex steroids, which may contribute to the increased complexity of the behavioral repertoires of dominant males.

    View details for DOI 10.1016/j.yhbeh.2006.09.008

    View details for Web of Science ID 000243645100021

    View details for PubMedID 17081541

  • Casting a genetic light on the evolution of eyes SCIENCE Fernald, R. D. 2006; 313 (5795): 1914-1918


    Light has been exploited for information by organisms through the evolution of photoreceptors and, ultimately, eyes in animals. Only a handful of eye types exist because the physics of light constrains photodetection. In the past few years, genetic tools have revealed several parallel pathways through which light guides behavior and have provided insights into the convergent evolution of eyes. The gene encoding opsin (the primary phototransduction protein) and some developmental genes had very early origins and were recruited repeatedly during eye evolution. Eye lens proteins arose separately and make up a diverse group, many of which were co-opted from other functions. A major challenge now is understanding how newly discovered pathways for processing light evolved and how they collaborate with eyes to harvest information from light.

    View details for DOI 10.1126/science.1127889

    View details for Web of Science ID 000240832200039

    View details for PubMedID 17008522

  • Physiological consequences of social descent: studies in Astatotilapia burtoni JOURNAL OF ENDOCRINOLOGY Parikh, V. N., Clement, T., Fernald, R. D. 2006; 190 (1): 183-190


    In many species, social interactions regulate reproductive capacity, although the exact mechanisms of such regulation are unclear. Since social stress is often related to reproductive regulation, we measured the physiological signatures of change in reproductive state as they relate to short-term stress and the stress hormone cortisol. We used an African cichlid fish, Astatotilapia burtoni, with two distinct, reversible male phenotypes: dominant (territorial, T) males that are larger, more brightly colored, more aggressive, and reproductively competent and non-dominant males (non-territorial, NT) that are smaller, camouflage colored, and have regressed gonads. Male status, and hence reproductive competence, depends on social experience in this system. Specifically, if a T male is placed among larger male fish, it quickly becomes NT in behavior and coloration, but complete regression of its reproductive axis takes ca. 3 weeks (White et al. 2002). Reproduction in all vertebrates is controlled by the hypothalamic-pituitary-gonadal axis in which the key signaling molecule from the brain to the pituitary is GnRH1. Here, we subjected T males to territory loss, a social manipulation which results in status descent. We measured the effects of this status change in levels of circulating cortisol and testosterone as well as mRNA levels of GnRH1 and GnRH receptor-1 (GnRH-R1) in the brain and pituitary, respectively. Following short-term social suppression (4 h), no change was observed in plasma cortisol level, GnRH1 mRNA expression, GnRH-R1 mRNA expression, or plasma testosterone level. However, following a somewhat longer social suppression (24 h), cortisol and GnRH1 mRNA levels were significantly increased, and testosterone levels were significantly decreased. These results suggest that in the short run, deposed T males essentially mount a neural 'defense' against loss of status.

    View details for DOI 10.1677/joe.1.06755

    View details for Web of Science ID 000239385600021

    View details for PubMedID 16837622

  • Differential social regulation of two pituitary gonadotropin-releasing hormone receptors BEHAVIOURAL BRAIN RESEARCH Au, T. M., Greenwood, A. K., Fernald, R. D. 2006; 170 (2): 342-346


    In many vertebrates, social interactions regulate reproductive capacity by altering the activity of the hypothalamic-pituitary-gonadal (HPG) axis. To better understand the mechanisms underlying social regulation of reproduction, we investigated the relationship between social status and one main component of the HPG axis: expression levels of gonadotropin-releasing hormone receptor (GnRH-R). Social interactions dictate reproductive capacity in the cichlid fish Astatotilapia burtoni. Reproductively active territory holders suppress the HPG axis of non-territorial males through repeated aggressive encounters. To determine whether the expression of GnRH-R is socially regulated, we quantified mRNA levels of two GnRH-R variants in the pituitaries and brains of territorial (T) and non-territorial (NT) A. burtoni males. We found that T males had significantly higher levels of pituitary GnRH-R1 mRNA than NT males. In contrast, GnRH-R2 mRNA levels in the pituitary did not vary with social status. Pituitaries from both T and NT males expressed significantly higher mRNA levels of GnRH-R1 than GnRH-R2. GnRH mRNA levels in the brain correlated positively with GnRH-R1 mRNA levels in the pituitary but did not correlate with pituitary GnRH-R2. Measurements of GnRH-R1 and GnRH-R2 mRNA levels across the whole brain revealed no social status differences. These results show that, in addition to the known effects of social status on other levels of the HPG axis, GnRH receptor in the pituitary is also a target of social regulation.

    View details for DOI 10.1016/j.bbr.2006.02.027

    View details for Web of Science ID 000238179500022

    View details for PubMedID 16580741

  • Chronic valproic acid treatment triggers increased neuropeptide Y expression and signaling in rat nucleus reticularis thalami JOURNAL OF NEUROSCIENCE Brill, J., Lee, M., Zhao, S., Fernald, R. D., Huguenard, J. R. 2006; 26 (25): 6813-6822


    Valproate (VPA) can suppress absence and other seizures, but its precise mechanisms of action are not completely understood. We investigated whether VPA influences the expression of neuropeptide Y (NPY), an endogenous anticonvulsant. Chronic VPA administration to young rats (300-600 in divided doses over 4 d) resulted in a 30-50% increase in NPY mRNA and protein expression in the nucleus reticularis thalami (nRt) and hippocampus, but not in the neocortex, as shown by real-time PCR, radioimmunoassay, and immunohistochemistry. No increased expression was observed after a single acute dose of VPA. Chronic treatment with the pharmacologically inactive VPA analog octanoic acid did not elicit changes in NPY expression. No significant expression changes could be shown for the mRNAs of the Y1 receptor or of the neuropeptides somatostatin, vasoactive intestinal polypeptide, and choleocystokinin. Fewer synchronous spontaneous epileptiform oscillations were recorded in thalamic slices from VPA-treated animals, and oscillation duration as well as the period of spontaneous and evoked oscillations were decreased. Application of the Y1 receptor inhibitor N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-D-arginine-amide (BIBP3226) enhanced thalamic oscillations, indicating that NPY is released during those oscillations and acts to downregulate oscillatory strength. Chronic VPA treatment significantly potentiated the effect of BIBP3226 on oscillation duration but not on oscillation period. These results demonstrate a novel mechanism for the antiepileptic actions of chronic VPA therapy.

    View details for DOI 10.1523/JNEUROSCI.5320-05.2006

    View details for Web of Science ID 000238473600018

    View details for PubMedID 16793888

  • Distributions of two gonadotropin-releasing hormone receptor types in a cichlid fish suggest functional specialization JOURNAL OF COMPARATIVE NEUROLOGY Chen, C. C., Fernald, R. D. 2006; 495 (3): 314-323


    Gonadotropin-releasing hormone 1 (GnRH1) from the brain controls reproduction in vertebrates via a GnRH-specific receptor in the pituitary; however, other forms of GnRH are found in all species, suggesting additional roles for this family of peptides. GnRH action depends critically on the location of its cognate receptors in the brain. To understand the potential roles of additional GnRH forms, we localized two known GnRH receptor types in a cichlid fish, Astatotilapia burtoni, in which GnRH1 is socially regulated. Using in situ hybridization, we describe the mRNA expression pattern of these GnRH receptor (GnRH-R) subtypes in the brain, specifically with respect to GnRH-producing neurons. Our data suggest that following a gene duplication, the two GnRH receptors have evolved to serve different functions. The type 1 receptor (GnRH-R1) is expressed less widely than the type 2 receptor (GnRH-R2). Specifically, GnRH-R1 is expressed in groups of neurons in the telencephalon, preoptic area, ventral hypothalamus, thalamus, and pituitary. In contrast, GnRH-R2 is expressed in many more brain areas, including the olfactory bulb, telencephalon, preoptic area, hypothalamus, thalamus, midbrain, optic tectum, cerebellum, hindbrain, and pituitary. The specific distribution of GnRH-R2 suggests that the GnRH ligands may act via this receptor to influence behavior in A. burtoni. Moreover, only GnRH-R2 mRNA is colocalized in the three known groups of GnRH-containing neurons, suggesting that any direct feedback regulation of GnRH by itself must act through this receptor type. Taken together, these data suggest that the two GnRH receptor types serve different functional roles in A. burtoni.

    View details for DOI 10.1002/cne.20827

    View details for Web of Science ID 000235463900005

    View details for PubMedID 16440293

  • Androgen level and male social status in the African cichlid, Astatotilapia burtoni BEHAVIOURAL BRAIN RESEARCH Parikh, V. N., Clement, T. S., Fernald, R. D. 2006; 166 (2): 291-295


    In vertebrates, circulating androgen levels are regulated by the hypothalamic-pituitary-gonadal (HPG) axis through which the brain controls the gonads via the pituitary. Androgen levels ultimately depend on factors including season, temperature, social circumstance, age, and other variables related to reproductive capacity and opportunity. Previous studies with an African cichlid fish, Astatotilapia burtoni, suggested that changes in both testosterone and 11-ketotestosterone (11-KT), an androgen specific to teleost fish, depend on male social status. Here we characterize circulating plasma concentrations of testosterone and 11-KT in socially dominant (territorial) and socially subordinate (non-territorial) males. Territorial males have significantly higher circulating levels of both forms of androgen, which is another defining difference between dominant and subordinate males in this species. These results underscore how internal and external cues related to reproduction are integrated at the level of the HPG axis.

    View details for DOI 10.1016/j.bbr.2005.07.011

    View details for Web of Science ID 000234643600014

    View details for PubMedID 16143408

  • Remodeling of the cone photoreceptor mosaic during metamorphosis of flounder (Pseudopleuronectes americanus) BRAIN BEHAVIOR AND EVOLUTION Hoke, K. L., Evans, B. I., Fernald, R. D. 2006; 68 (4): 241-254


    The retinal cone mosaic of the winter flounder, Pseudopleuronectes americanus, is extensively remodeled during metamorphosis when its visual system shifts from monochromatic to trichromatic. Here we describe the reorganization and re-specification of existing cone subtypes in which larval cones alter their spatial arrangement, morphology, and opsin expression to determine whether mechanisms controlling cell birth, mosaic position, and opsin selection are coordinated or independent. We labeled dividing cells with tritiated ((3)H) thymidine prior to mosaic remodeling to determine whether existing cone photoreceptors change phenotype. We also used in situ hybridization to identify mosaic type and opsin expression in transitional retinas to understand the sequence of transformation. Our data indicate that in the winter flounder retina the choice of new opsin species and the cellular rearrangement of the mosaic proceed independently. The production of the precise cone mosaic arrangement is not due to a stereotyped series of sequential cellular inductions, but rather might be the product of a set of distinct, flexible processes that rely on plasticity in cell phenotype.

    View details for DOI 10.1159/000094705

    View details for Web of Science ID 000241944600004

    View details for PubMedID 16864981

  • Investigator profile. An interview with Russell D. Fernald, Ph.D. Interview by Vicki Glaser. Zebrafish Fernald, R. D. 2006; 3 (2): 119-125


    Russell D. Fernald, Ph.D., is a Professor of Biological Sciences and the Benjamin Scott Crocker Professor in Human Biology at Stanford University (California). He received his Bachelor's degree from Swarthmore College (Swarthmore, PA) and his Ph.D. from the University of Pennsylvania (Philadelphia). Dr. Fernald completed a postdoctoral fellowship with Dr. O. Creutzfeldt at the Max-Planck-Institute for Psychiatry, in Munich, Germany, and a postdoctoral fellowship with Dr. Konrad Lorenz at the Max-Planck-Institute for Behavioral Physiology. In 2004 he shared the Rank Prize for discoveries about lens function. Dr. Fernald's lab uses an African cichlid fish species to study how social experience influences the brain and how retinal progenitor cell division and differentiation are controlled.

    View details for DOI 10.1089/zeb.2006.3.119

    View details for PubMedID 18248254

  • Rapid behavioral and genomic responses to social opportunity PLOS BIOLOGY Burmeister, S. S., Jarvis, E. D., Fernald, R. D. 2005; 3 (11): 1996-2004


    From primates to bees, social status regulates reproduction. In the cichlid fish Astatotilapia (Haplochromis) burtoni, subordinate males have reduced fertility and must become dominant to reproduce. This increase in sexual capacity is orchestrated by neurons in the preoptic area, which enlarge in response to dominance and increase expression of gonadotropin-releasing hormone 1 (GnRH1), a peptide critical for reproduction. Using a novel behavioral paradigm, we show for the first time that subordinate males can become dominant within minutes of an opportunity to do so, displaying dramatic changes in body coloration and behavior. We also found that social opportunity induced expression of the immediate-early gene egr-1 in the anterior preoptic area, peaking in regions with high densities of GnRH1 neurons, and not in brain regions that express the related peptides GnRH2 and GnRH3. This genomic response did not occur in stable subordinate or stable dominant males even though stable dominants, like ascending males, displayed dominance behaviors. Moreover, egr-1 in the optic tectum and the cerebellum was similarly induced in all experimental groups, showing that egr-1 induction in the anterior preoptic area of ascending males was specific to this brain region. Because egr-1 codes for a transcription factor important in neural plasticity, induction of egr-1 in the anterior preoptic area by social opportunity could be an early trigger in the molecular cascade that culminates in enhanced fertility and other long-term physiological changes associated with dominance.

    View details for DOI 10.1371/journal.pbio.0030363

    View details for Web of Science ID 000233609300019

    View details for PubMedID 16216088

  • Comprehensive algorithm for quantitative real-time polymerase chain reaction JOURNAL OF COMPUTATIONAL BIOLOGY Zhao, S., Fernald, R. D. 2005; 12 (8): 1047-1064


    Quantitative real-time polymerase chain reactions (qRT-PCR) have become the method of choice for rapid, sensitive, quantitative comparison of RNA transcript abundance. Useful data from this method depend on fitting data to theoretical curves that allow computation of mRNA levels. Calculating accurate mRNA levels requires important parameters such as reaction efficiency and the fractional cycle number at threshold (CT) to be used; however, many algorithms currently in use estimate these important parameters. Here we describe an objective method for quantifying qRT-PCR results using calculations based on the kinetics of individual PCR reactions without the need of the standard curve, independent of any assumptions or subjective judgments which allow direct calculation of efficiency and CT. We use a four-parameter logistic model to fit the raw fluorescence data as a function of PCR cycles to identify the exponential phase of the reaction. Next, we use a three-parameter simple exponent model to fit the exponential phase using an iterative nonlinear regression algorithm. Within the exponential portion of the curve, our technique automatically identifies candidate regression values using the P-value of regression and then uses a weighted average to compute a final efficiency for quantification. For CT determination, we chose the first positive second derivative maximum from the logistic model. This algorithm provides an objective and noise-resistant method for quantification of qRT-PCR results that is independent of the specific equipment used to perform PCR reactions.

    View details for Web of Science ID 000233288200001

    View details for PubMedID 16241897

  • Diurnal rhythm of cone opsin expression in the teleost fish Haplochromis burtoni VISUAL NEUROSCIENCE Halstenberg, S., Lindgren, K. M., Samagh, S. P., Nadal-Vicens, M., Balt, S., Fernald, R. D. 2005; 22 (2): 135-141


    The biochemical and morphological specializations of rod and cone photoreceptors reflect their roles in sight. The apoprotein opsin, which converts photons into chemical signals, functions at one end of these highly polarized cells, in the outer segment. Previous work has shown that the mRNA of rod opsin, the opsin specific to rods, is renewed in the outer segment with a diurnal rhythm in the retina of the teleost fish Haplochromis burtoni. Here we show that in the same species, all three cone opsin mRNAs (blue, green, and red) also have a diurnal rhythm of expression. Quantitative real-time polymerase chain reaction (PCR) with primer pairs specific for the cone photoreceptor opsin subtypes was used to detect opsin mRNA abundance in animals sacrificed at 3-h intervals around the clock. All three cone opsins were expressed with diurnal rhythms similar to each other but out of phase with the rod opsin rhythm. Specifically, cone opsin expression occurs at a higher level near the onset of the dark period, when cones are not used for vision. Finally, we found that the rhythm of cone opsin expression in fish appears to be light dependent, as prolonged darkness changes normal diurnal expression patterns.

    View details for DOI 10.1017/S09522523805222022

    View details for Web of Science ID 000229671300002

    View details for PubMedID 15935106

  • Behavioral coping strategies in a cichlid fish: the role of social status and acute stress response in direct and displaced aggression HORMONES AND BEHAVIOR Clement, T. S., Parikh, V., Schrumpf, M., Fernald, R. D. 2005; 47 (3): 336-342


    The African cichlid fish, Astatotilapia burtoni, has a complex social system with a sophisticated social hierarchy that offers unique opportunities to understand how social rank and its physiological substrates relate to behavioral strategies. In A. burtoni, a small fraction of the males are dominant (T, territorial), as distinguished by being large, brightly colored, reproductively active, and aggressively defending territories. In contrast, the majority of males are non-dominant (NT, non-territorial), being smaller, drably colored, sexually immature, and typically schooling with females. The social system is regulated by aggressive interactions between males and behavioral responses to aggression can be direct or displaced with respect to the animal that acts. To determine whether direct and displaced behaviors are differentially exhibited by T and NT males, individuals were shown a video presentation of a dominant male displaying aggressively. Analysis of aggressive acts toward the video display and displaced activity toward a tank mate revealed that T males exhibited more direct behavior (toward the video display), while NT males engaged in more displaced behavior (toward tank mates). Because similar experiments with primates suggest that shifts in behavioral strategies are linked to changes in the stress response (as measured by circulating cortisol levels), we measured cortisol levels of T and NT males following exposure to the aggressive stimulus. Although in some animals subordinate males are reported to have higher cortisol levels, here we show that in A. burtoni the endocrine response to specific situations can vary considerably even among animals of the same status. Interestingly, NT males with intermediate cortisol levels showed more directed behavior while NT males with both high and low cortisol levels showed more displaced. This suggests an optimal physiological stress response in NT males that predisposes them to challenge aggressors perhaps making it more likely for them to ascend in status.

    View details for DOI 10.1016/j.yhbeh.2004.11.014

    View details for Web of Science ID 000227326100013

    View details for PubMedID 15708763

  • Evolutionary conservation of the Egr-1 immediate-early gene response in a teleost JOURNAL OF COMPARATIVE NEUROLOGY Burmeister, S. S., Fernald, R. D. 2005; 481 (2): 220-232


    Immediate-early gene expression is a key part of a neuron's response to behaviorally relevant stimuli and, as a result, localization of immediate-early gene expression can be a useful marker for neural activity. We characterized the immediate-early gene egr-1 (also called zif268, NGFI-A, krox-24, ZENK) in the teleost Astatotilapia (Haplochromis) burtoni. We compared the A. burtoni egr-1 predicted protein sequence to that of other vertebrates, characterized its gene expression time course, and localized its induced expression throughout the brain. The A. burtoni egr-1 predicted protein shared putative functional domains with egr-1 of other vertebrates and shared 81% sequence similarity with zebrafish and 66% with mouse. We identified distinct mammalian and teleost inserts rich in serine residues within one activation domain, suggesting convergent responses to selection pressures to increase the number of serine residues in this region. Functionally, we found that A. burtoni egr-1 gene expression peaked near 30 minutes after pharmacological stimulation and thereby displayed the transient expression above basal levels characteristic of egr-1 expression in birds and mammals. Finally, we observed distinct patterns of egr-1 gene induction in the brain by natural and pharmacological stimuli. Unstimulated males had very low expression levels of egr-1, whereas males stimulated by their normal environment showed higher levels of expression specific to particular brain regions. Males injected with a glutamate receptor agonist also had region-specific induction of egr-1 expression. We conclude that the egr-1 immediate-early gene response is evolutionarily conserved and will, therefore, be useful for identifying functional neural responses in nontraditional model species.

    View details for DOI 10.1002/cne.20380

    View details for Web of Science ID 000225561800006

    View details for PubMedID 15562507

  • IGF-1 produced by cone photoreceptors regulates rod progenitor proliferation in the teleost retina DEVELOPMENTAL BRAIN RESEARCH Zygar, C. A., Colbert, S., Yang, D., Fernald, R. D. 2005; 154 (1): 91-100


    Teleost eyes grow throughout life by adding neurons and stretching extant tissue. New retinal neurons of all types are added at the ciliary margin and new rod photoreceptors are inserted throughout retina in the outer nuclear layer (ONL). New rod photoreceptors result from the division of progenitor cells located in the ONL amidst functioning rod photoreceptor cell nuclei, but it is not known how new rod addition is regulated. Previous experiments using an organotypic retinal slice preparation revealed that insulin-like growth factor 1 (IGF-1) up-regulates the division of the rod progenitor cells [Dev. Brain Res. 76 (1993) 183], but the site of IGF-1 action was unknown. Here, we show where in the retina IGF-1 is made, where IGF receptors are located, and we identify the role of IGF-1 in adult retinal rod neurogenesis with both gain-and loss-of-function experiments. We found that IGF-1 is expressed by cone photoreceptor cells and its abundance varies with a daily rhythm, being significantly higher at night. In vivo application of exogenous IGF-1 increases rod progenitor cell division, an effect that is greater at night than during the day. We also show that inhibiting the function of IGF receptors decreases proliferation of rod progenitor cells. Finally, we show that IGF receptors are located on rod progenitor cells as well as on cone and rod photoreceptors. Taken together, these data suggest that the rhythmic production and release of IGF-1 plays a role in regulating the insertion of new rod photoreceptors into the retina. The diurnal change in IGF-1 abundance and effects of exogenous IGF-1 are consistent with the previous demonstration that rod progenitor cell division is threefold greater at night than in the day [Brain Res. 673 (1995) 119; Brain Res. 712 (1996) 40]. We also show that the insertion of new rod photoreceptors at the central edge of the ciliary neurogenic zone very likely also depends on IGF-1 production by cone photoreceptors. We propose that addition of new rod photoreceptors into the functioning retina is regulated through a feedback mechanism mediated at least in part via the IGF-1 produced in the cone photoreceptors.

    View details for DOI 10.1016/j.devbraines.204.10.009

    View details for Web of Science ID 000226434800010

    View details for PubMedID 15617759

  • Female affiliative preference depends on reproductive state in the African cichlid fish, Astatotilapia burtoni BEHAVIORAL ECOLOGY Clement, T. S., Grens, K. E., Fernald, R. D. 2005; 16 (1): 83-88
  • Two visual processing pathways are targeted by gonadotropin-releasing hormone in the retina BRAIN BEHAVIOR AND EVOLUTION Grens, K. E., Greenwood, A. K., Fernald, R. D. 2005; 66 (1): 1-9


    In fish the terminal nerve is comprised of a group of cells with somata adjacent to the olfactory bulb and processes that extend both anteriorly to the olfactory mucosa and posteriorly to the telencephalon. In teleost fish an additional group of axons extends along the optic tract and delivers putative neuromodulators to the retina. One peptide - gonadotropin-releasing hormone (GnRH) - has been implicated as a prime candidate neuromodulator based on electrophysiological evidence that exogenous application influences neural activity. Here we describe the expression patterns of two GnRH receptor subtypes in the retina of a teleost fish, Astatotilapia (Haplochromis) burtoni. The type 1 GnRH receptor (GnRH-R1) was expressed in cells of the amacrine cell layer - where lateral inputs affect the flow of visual information from photoreceptors to the brain - and in a distribution and location pattern similar to dopaminergic interplexiform cells. Immunohistochemical labeling of GnRH fibers revealed varicosities along terminal nerve axons near the amacrine cell layer and near cells immunoreactive for tyrosine hydroxylase, a dopaminergic cell marker. This finding supports an existing model that the terminal nerve forms synapses with dopaminergic interplexiform cells. Surprisingly, the type 2 GnRH receptor (GnRH-R2) was abundantly expressed in ganglion cells, which lie along the direct pathway of visual information to the brain. These data suggest that GnRH from the TN could broadly influence processing of retinal signals both in lateral processing circuits through GnRH-R1 and in the vertical throughput pathway through GnRH-R2.

    View details for DOI 10.1159/000085043

    View details for Web of Science ID 000229034100001

    View details for PubMedID 15821344

  • Functional mapping of the auditory midbrain during mate call reception JOURNAL OF NEUROSCIENCE Hoke, K. L., Burmeister, S. S., Fernald, R. D., Rand, A. S., Ryan, M. J., Wilczynski, W. 2004; 24 (50): 11264-11272


    We examined patterns of neural activity as assayed by changes in gene expression to localize representation of acoustic mating signals in the auditory midbrain of frogs. We exposed wild-caught male Physalaemus pustulosus to conspecific mating calls that vary in their behavioral salience, nonsalient mating calls, or no sound. We measured expression of the immediate early gene egr-1 (also called ZENK, zif268, NGFI-A, and krox-24) throughout the torus semicircularis, the auditory midbrain homolog of the inferior colliculus. Differential egr-1 induction in response to the acoustic stimuli occurred in the laminar, midline, and principal nuclei of the torus semicircularis, whereas the ventral region did not show significant effects of stimulus. The laminar nucleus differentially responded to conspecific mating calls compared with nonsalient mating calls, whereas the midline and principal nuclei responded preferentially to one of two conspecific calls. These responses were not explained by simple acoustic properties of the stimuli, and they demonstrate a functional heterogeneity of auditory processing of complex biological signals within the frog midbrain. Moreover, using analyses that assess the ability of the torus semicircularis as a whole to discriminate among acoustic stimuli, we found that activity patterns in the four regions together provide more information about biologically relevant acoustic stimuli than activity in any single region.

    View details for DOI 10.1523/JNEUROSCI.2079-04.2004

    View details for Web of Science ID 000225766200010

    View details for PubMedID 15601932

  • Social regulation of the electrical properties of gonadotropin-releasing hormone neurons in a Cichlid fish (Astatotilapia burtoni) BIOLOGY OF REPRODUCTION Greenwood, A. K., Fernald, R. D. 2004; 71 (3): 909-918


    Variation in reproductive capacity is common across the lives of all animals. In vertebrates, hypothalamic neurons that secrete GnRH are a primary mediator of such reproductive plasticity. Since social interactions suppress gonadal maturity in the African cichlid fish, Astatotilapia (Haplochromis) burtoni, we investigated whether the electrical properties of GnRH neurons were also socially regulated. Adult A. burtoni males are either territorial (T) and reproductively active or nonterritorial (NT) and reproductively regressed, depending upon their social environment. We compared the basic electrical properties of hypothalamic GnRH neurons from T and NT males using whole-cell electrophysiology in vitro. GnRH neurons were spontaneously active and exhibited several different activity patterns. A small fraction of neurons exhibited episodic activity patterns, which have been described in GnRH neurons from mammals. The type of activity pattern and spontaneous firing rate did not vary with reproductive capacity; however, several basic electrical properties were different. Neurons from T males were larger than those from NT males and had higher membrane capacitance and lower input resistance. In neurons from NT males, action potential duration was significantly longer and after-hyperpolarization characteristics were diminished, which led to a tendency for neurons from NT males to fire less rapidly in response to current injection. We predict this could serve to decrease GnRH release in NT males. These data are the first electrophysiological characterization of hypothalamic GnRH neurons in a nonmammalian species and provide evidence for several changes in electrical properties with reproductive state.

    View details for DOI 10.1095/biolreprod.104.030072

    View details for Web of Science ID 000223541200025

    View details for PubMedID 15140799

  • Timing and location of rhodopsin expression in newly born rod photoreceptors in the adult teleost retina DEVELOPMENTAL BRAIN RESEARCH Henderson, R. G., Fernald, R. D. 2004; 151 (1-2): 193-197


    Labeling of newly divided retinal cells with bromodeoxyuridine (BrdU) and a rhodopsin mRNA probe revealed that rhodopsin is first expressed by new rod photoreceptors 2 days after cell birth in an adult cichlid fish. Most new cells that expressed rhodopsin had nuclei located in the vitreal half of the outer nuclear layer (ONL), lending further support to the hypothesis that movement from scleral to vitreal ONL is associated with rod differentiation.

    View details for DOI 10.1016/j.devbrainres.2004.04.001

    View details for Web of Science ID 000222960200019

    View details for PubMedID 15246705

  • Eyes: Variety, development and evolution BRAIN BEHAVIOR AND EVOLUTION Fernald, R. D. 2004; 64 (3): 141-147


    The selective advantages of using light as a source of information are reflected in the diverse types of extant eyes. The physical properties of light restrict how it can be collected and processed, resulting in only eight known optical systems found in animals. Eyes develop through tissue rearrangement and differentiation. Our understanding of the source of genetic information used in developmental programs is growing rapidly and reveals distributions of gene expression with substantial overlap in both time and space. Specific genes and their products are used repeatedly, making causal relationships more difficult to discern. The phenomenon of groups of genes acting together seems to be the rule. Throughout evolution, particular genes have become associated with distinct aspects of eye development, and these suites of genes have been recruited repeatedly as new eyes evolved.

    View details for DOI 10.1159/000079743

    View details for Web of Science ID 000223758800003

    View details for PubMedID 15353906

  • How the brain processes social information: Searching for the social brain ANNUAL REVIEW OF NEUROSCIENCE Insel, T. R., Fernald, R. D. 2004; 27: 697-722


    Because information about gender, kin, and social status are essential for reproduction and survival, it seems likely that specialized neural mechanisms have evolved to process social information. This review describes recent studies of four aspects of social information processing: (a) perception of social signals via the vomeronasal system, (b) formation of social memory via long-term filial imprinting and short-term recognition, (c) motivation for parental behavior and pair bonding, and (d) the neural consequences of social experience. Results from these studies and some recent functional imaging studies in human subjects begin to define the circuitry of a "social brain." Such neurodevelopmental disorders as autism and schizophrenia are characterized by abnormal social cognition and corresponding deficits in social behavior; thus social neuroscience offers an important opportunity for translational research with an impact on public health.

    View details for DOI 10.1146/annurev.neuro.27.070203.144148

    View details for Web of Science ID 000223246300025

    View details for PubMedID 15217348

  • Evolving eyes INTERNATIONAL JOURNAL OF DEVELOPMENTAL BIOLOGY Fernald, R. D. 2004; 48 (8-9): 701-705


    Despite the incredible diversity among extant eyes, laws of physics constrain how light can be collected resulting in only eight known optical systems in animal eyes. Surprisingly, all animal eyes share a common molecular strategy using opsin for catching photons, but there are a diverse collection of mechanisms with proteins unrelated to each other used to focus light for vision. However, opsin is expressed in either one of two types of photoreceptor that differ fundamentally in their structure and tissue of origin. Taken together, this collection of observations strongly suggests that eyes have had multiple origins with remarkable convergence due to physics and molecular conservation of the opsin protein. Yet recent work has shown that a family of conserved genes are involved in eye formation despite substantial differences in their structure and origin, leading to a controversy over whether eyes evolved once or repeatedly. A likely resolution of this discussion is that particular genes and genetic programs have become associated with specific features needed for eyes and such suites of genes have been recruited as new eyes evolve. Since specific genes and their products are used repeatedly, it is somewhat difficult to conceptualize their causal relationships relative to evolutionary processes. However, detailed comparison of developmental programs may offer clues about multiple origins.

    View details for DOI 10.1387/ijdb.041888rf

    View details for Web of Science ID 000225958100004

    View details for PubMedID 15558462

  • How does behavior change the brain? Multiple methods to answer old questions Fernald, R. D. OXFORD UNIV PRESS INC. 2003: 771-779


    Clearly the brain controls behavior but can behavior also "control" the brain? On an evolutionary time scale, selective ecological pressures shape the sensory and motor capacities as well as the body and behavior. Correspondingly, in development, behavior acts in concert with the environment to cause structural changes in the brain lasting a lifetime. Surprisingly, in "real time" social behavior can also cause changes, typically reversible, in the brain in adult animals. Changes caused by behavioral interactions can be dramatic, and in many instances, these interactions are directly related to reproductive behavior. Understanding how behavior sculpts the brain in the course of behavioral interactions is a major challenge. Analyzing such changes requires a model system allowing control of the biological and behavioral environment of many animals simultaneously yet allowing access to physiological, cellular and molecular processes being regulated. The mouthbrooding cichlid Haplochromis (Astatotilapia) burtoni (Günther) from Lake Tanganyika lends itself to the study of social influences on the brain. It has complex, though easily observable individual and social behaviors regulated by two distinct classes of males, those with territories and those without. Many features of the animals are shaped by social encounters including the maturation of juveniles, the hypothalamic-pituitary-gonadal axis, the growth rate, the basal stress level among others. How does social information effect change in the brain and body? Animals must attend to the social scene to identify their chances. Learning how social information is transduced into cellular changes in this species should help understand how this happens in other social animals.

    View details for Web of Science ID 000222235200001

    View details for PubMedID 21680475

  • The regulatory effects of cortisol on social status shift in Haplochromis burtoni Parikh, V. N., Schrumpf, M., Clement, T., Fernald, R. D. OXFORD UNIV PRESS INC. 2003: 879-879
  • Multiple corticosteroid receptors in a teleost fish: Distinct sequences, expression patterns, and transcriptional activities ENDOCRINOLOGY Greenwood, A. K., Butler, P. C., White, R. B., DeMarco, U., Pearce, D., Fernald, R. D. 2003; 144 (10): 4226-4236


    Corticosteroid hormones, including the mineralocorticoids and the glucocorticoids, regulate diverse physiological functions in vertebrates. These hormones act through two classes of corticosteroid receptors (CR) that are ligand-dependent transcription factors: type I or mineralocorticoid receptor (MR) and type II or glucocorticoid receptor (GR). There is substantial overlap in the binding of these two receptor types to hormones and to DNA. In fish, the overlap in processes controlled by CRs may be different from that in other vertebrates, as fish are thought to synthesize only glucocorticoids, whereas they express both GR and MR. Here we describe the characterization of four CRs in a cichlid fish, Haplochromis burtoni: a previously undescribed GR (HbGR1), another GR expressed in two splice isoforms (HbGR2a and HbGR2b), and an MR (HbMR). Sequence comparison and phylogenetic analysis showed that these CRs sort naturally into GR and MR groups, and that the GR duplication we describe will probably be common to all teleosts. Quantitative PCR revealed differential patterns of CR tissue expression in organs dependent on corticosteroid action. Trans-activation assays demonstrated that the CRs were selective for corticosteroid hormones and showed that the HbMR was similar to mammalian MRs in being more sensitive to both cortisol and aldosterone than the GRs. Additionally, the two HbGR2 isoforms were expressed uniquely in different tissues and were functionally distinct in their actions on classical GR-sensitive promoters. The identification of four CR subtypes in teleosts suggests a more complicated corticosteroid signaling in fish than previously recognized.

    View details for DOI 10.1210/en.2003-0566

    View details for Web of Science ID 000185429500002

    View details for PubMedID 12959971

  • Social regulation of gonadotropin-releasing hormone JOURNAL OF EXPERIMENTAL BIOLOGY White, S. A., Nguyen, T., Fernald, R. D. 2002; 205 (17): 2567-2581


    Behavioral interactions among social animals can regulate both reproductive behavior and fertility. A prime example of socially regulated reproduction occurs in the cichlid fish Haplochromis burtoni, in which interactions between males dynamically regulate gonadal function throughout life. This plasticity is mediated by the brain, where neurons that contain the key reproductive regulatory peptide gonadotropin-releasing hormone (GnRH) change size reversibly depending on male social status. To understand how behavior controls the brain, we manipulated the social system of these fish, quantified their behavior and then assessed neural and physiological changes in the reproductive and stress axes. GnRH gene expression was assessed using molecular probes specific for the three GnRH forms in the brain of H. burtoni. We found that perception of social opportunity to increase status by a male leads to heightened aggressiveness, to increased expression of only one of the three GnRH forms and to increases in size of GnRH-containing neurons and of the gonads. The biological changes characteristic of social ascent happen faster than changes following social descent. Interestingly, behavioral changes show the reverse pattern: aggressive behaviors emerge more slowly in ascending animals than they disappear in descending animals. Although the gonads and GnRH neurons undergo similar changes in female H. burtoni, regulation occurs via endogenous rather than exogenous social signals. Our data show that recognition of social signals by males alters stress levels, which may contribute to the alteration in GnRH gene expression in particular neurons essential for the animal to perform in its new social status.

    View details for Web of Science ID 000177957500002

    View details for PubMedID 12151363

  • Social regulation of the brain: sex, size and status Fernald, R. D. JOHN WILEY & SONS LTD. 2002: 169-186


    Fish comprise the largest group of extant vertebrates with approximately 25,000 known species. Some of these species are exceptional among vertebrates because they can change sex as adults. This observation raises ultimate questions about what selective forces led to the evolution of sex-changing ability and raises proximate questions about what mechanisms could account for this process. Sex change can be either from female to male (protogyny) or the reverse (protandry). In either case, the actual process of sex reversal requires reorganization of many critically important physiological systems from transformation of the gonads to modification of the neural and hormonal control systems. All of these changes require an individual animal to initiate the process based on information gleaned from the social situation. This is all the more remarkable because the information could be as simple as size discrimination or as complex as detecting subtle behavioural signals. Although it is self-evident that the brain controls behaviour, clearly behaviour can also 'control' the brain. How does behaviour cause changes in the brain? The work described here links molecular events with organismal behaviour by using an African cichlid fish model system in which social behaviours regulate reproduction. These animals have a complex social system based on the behaviour of two distinct classes of males, those with territories and those without. Changes in social status produced by behavioural interactions cause changes in neurons and endocrine responses. Surprisingly, growth rate is also regulated by social status and prior social history. Discovering how relevant social information is transduced into physiological processes requiring cellular and molecular action presents a major challenge.

    View details for Web of Science ID 000176917700012

    View details for PubMedID 11990790

  • Gonadotropin-releasing hormone receptor in the teleost Haplochromis burtoni: Structure, location, and function ENDOCRINOLOGY Robison, R. R., White, R. B., Illing, N., Troskie, B. E., Morley, M., Millar, R. P., Fernald, R. D. 2001; 142 (5): 1737-1743


    GnRH acts via GnRH receptors (GnRH-R) in the pituitary to cause the release of gonadotropins that regulate vertebrate reproduction. In the teleost fish, Haplochromis burtoni, reproduction is socially regulated through the hypothalamus-pituitary-gonadal axis, making the pituitary GnRH-R a likely site of action for this control. As a first step toward understanding the role of GnRH-R in the social control of reproduction, we cloned and sequenced candidate GnRH-R complementary DNAs from H. burtoni tissue. We isolated a complementary DNA that predicts a peptide encoding a G protein-coupled receptor that shows highest overall identity to other fish type I GnRH-R (goldfish IA and IB and African catfish). Functional testing of the expressed protein in vitro confirmed high affinity binding of multiple forms of GNRH: Localization of GnRH-R messenger RNA using RT-PCR revealed that it is widely distributed in the brain and retina as well as elsewhere in the body. Taken together, these data suggest that this H. burtoni GnRH receptor probably interacts in vivo with all three forms of GNRH:

    View details for Web of Science ID 000168434500009

    View details for PubMedID 11316736

  • The development of the crystalline lens is sensitive to visual input in the African cichlid fish, Haplochromis burtoni VISION RESEARCH Kroger, R. H., Campbell, M. C., Fernald, R. D. 2001; 41 (5): 549-559


    We investigated whether the development of the vertebrate crystalline lens is sensitive to visual input. The optical properties of fish lenses were examined as a function of lens size and the optical rearing conditions. Fish (Haplochromis burtoni, Cichlidae) were reared in white light (control group), under spectral deprivation (monochromatic lights), deprivation of the cone system (scotopic illumination), and complete visual deprivation (darkness). Longitudinal spherical aberrations (LSAs) and refractive index profiles of the lenses were measured with thin laser beams. The performance of the lens was modeled by ray-tracing calculations from measured LSAs. In lenses from the control group, LSA and f/R (focal length relative to lens radius) decreased as a function of age. The optical properties of the lenses were modified after rearing in darkness, scotopic illumination, and in monochromatic lights due to changes in the refractive index profile. Rearing in darkness and scotopic illumination reduced the optical quality of the lens. In animals reared under spectral deprivation, the lens did not create well-focused images for all spectral cone types in the same plane, as it does in animals reared in white light. We conclude that visual input seems to play an important role in the development of the lens. The control mechanisms remain unknown.

    View details for Web of Science ID 000167420900002

    View details for PubMedID 11226501

  • Evolution of eyes CURRENT OPINION IN NEUROBIOLOGY Fernald, R. D. 2000; 10 (4): 444-450


    Seeing is important for most species and it has been a key selective advantage throughout evolution. Consequently, there is a remarkable diversity among types of eyes. Animals have converged on eight optical solutions for collecting and focusing light; in contrast, all eyes share the same molecular strategy for absorbing photons. Recent studies have identified similarities in the genetic information that is used in the development of eyes, leading to the hypothesis that distinctly different eye types might have had a monophyletic origin. Across many species, there is a remarkable continuity of the developmental genes that participate in the construction of similar--but not necessarily homologous--eyes.

    View details for Web of Science ID 000088700300003

    View details for PubMedID 10981612

  • Social status controls somatostatin neuron size and growth JOURNAL OF NEUROSCIENCE Hofmann, H. A., Fernald, R. D. 2000; 20 (12): 4740-4744


    Many animal species show flexible behavioral responses to environmental and social changes. Such responses typically require changes in the neural substrate responsible for particular behavioral states. We have shown previously in the African cichlid fish, Haplochromis burtoni, that changes in social status, including events such as losing or winning a territorial encounter, result in changes in somatic growth rate. Here we demonstrate for the first time that changes in social status cause changes in the size of neurons involved in the control of growth. Specifically, somatostatin-containing neurons in the hypothalamus of H. burtoni increase up to threefold in volume in dominant and socially descending animals compared with cell sizes in subordinate and socially ascending fish. Because somatostatin is known to be an inhibitor of growth hormone release, the differences in cell size suggest a possible mechanism to account for the more rapid growth rates of subordinate and socially ascending animals compared with those of dominant or socially descending fish. These results reveal possible mechanisms responsible for socially induced physiological plasticity that allow animals to shift resources from reproduction to growth or vice versa depending on the social context.

    View details for Web of Science ID 000087448500041

    View details for PubMedID 10844043

  • Two molecular forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II) are expressed by two separate populations of cells in the rhesus macaque hypothalamus MOLECULAR BRAIN RESEARCH Latimer, V. S., Rodrigues, S. M., Garyfallou, V. T., Kohama, S. G., White, R. B., Fernald, R. D., Urbanski, H. F. 2000; 75 (2): 287-292


    Gonadotropin-releasing hormone represents the primary neuroendocrine link between the brain and the reproductive axis, and at least two distinct molecular forms of this decapeptide (GnRH-I and GnRH-II) are known to be expressed in the forebrain of rhesus macaques (Macaca mulatta). Although the distribution pattern of the two corresponding mRNAs is largely dissimilar, their expression appears to show some overlap in specific regions of the hypothalamus; this raises the possibility that some cells express both molecular forms of GnRH. To resolve this issue, double-label histochemistry was performed on hypothalamic sections from six male rhesus macaques, using a monoclonal antibody to GnRH-I and a riboprobe to monkey GnRH-II mRNA. In total, more than 2000 GnRH neurons were examined but in no instance were GnRH-I peptide and GnRH-II mRNA found to be coexpressed. This finding emphasizes that GnRH-I and GnRH-II are synthesized by two distinct populations of hypothalamic neurons, and suggests that they may be regulated by different neuroendocrine pathways.

    View details for Web of Science ID 000085564400013

    View details for PubMedID 10686350

  • Social status regulates growth rate: Consequences for life-history strategies PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Hofmann, H. A., Benson, M. E., Fernald, R. D. 1999; 96 (24): 14171-14176


    The life-history strategies of organisms are sculpted over evolutionary time by the relative prospects of present and future reproductive success. As a consequence, animals of many species show flexible behavioral responses to environmental and social change. Here we show that disruption of the habitat of a colony of African cichlid fish, Haplochromis burtoni (Günther) caused males to switch social status more frequently than animals kept in a stable environment. H. burtoni males can be either reproductively active, guarding a territory, or reproductively inactive (nonterritorial). Although on average 25-50% of the males are territorial in both the stable and unstable environments, during the 20-week study, nearly two-thirds of the animals became territorial for at least 1 week. Moreover, many fish changed social status several times. Surprisingly, the induced changes in social status caused changes in somatic growth. Nonterritorial males and animals ascending in social rank showed an increased growth rate whereas territorial males and animals descending in social rank slowed their growth rate or even shrank. Similar behavioral and physiological changes are caused by social change in animals kept in stable environmental conditions, although at a lower rate. This suggests that differential growth, in interaction with environmental conditions, is a central mechanism underlying the changes in social status. Such reversible phenotypic plasticity in a crucial life-history trait may have evolved to enable animals to shift resources from reproduction to growth or vice versa, depending on present and future reproductive prospects.

    View details for Web of Science ID 000083872900103

    View details for PubMedID 10570217

  • Nasotemporal asymmetry during teleost retinal growth: Preserving an area of specialization JOURNAL OF NEUROBIOLOGY Zygar, C. A., Lee, M. J., Fernald, R. D. 1999; 41 (3): 435-442


    Teleost fish retinas grow throughout adult life through both cell addition and stretching. Cell division occurs at the periphery of the retina, resulting in annular addition of all cell types except rod photoreceptors, which are added in the central retina. Since many teleosts have a region of high cellular density at the temporal pole of the eye, we analyzed whether and how this specialized region of high visual acuity maintained its relative topographical position through asymmetric circumferential growth. To do this, we measured the pattern of long-term retinal growth in the African cichlid Haplochromis burtoni. We found that the retina expands asymmetrically along the nasotemporal axis, with the nasal retina growing at a higher rate than the temporal, dorsal, or ventral retinae, whose growth rates are equal. This nasotemporal asymmetry is produced via significantly greater expansion of retinal tissue at the nasal pole rather than through differential cell proliferation. The mechanisms responsible for this differential retinal enlargement are unknown; however, such asymmetric expansion very likely minimizes disruption in vision during rapid growth.

    View details for Web of Science ID 000083420400011

    View details for PubMedID 10526321

  • Gonadotropin-releasing hormone genes: Phylogeny, structure, and functions FRONTIERS IN NEUROENDOCRINOLOGY Fernald, R. D., White, R. B. 1999; 20 (3): 224-240


    Gonadotropin-releasing hormone (GnRH, previously called leutinizing hormone-releasing hormone, LHRH) is the final common signaling molecule used by the brain to regulate reproduction in all vertebrates. Recently, genes encoding two other GnRH forms have been discovered. Here we present a phylogenetic analysis that shows that the GnRH genes fall naturally into three distinct branches, each of which shares not only a molecular signature but also characteristic expression sites in the brain. The GnRH genes appear to have arisen through gene duplication from a single ancestral GnRH whose origin predates vertebrates. Several lines of data support this suggestion, including the fact that all three genes share an identical exonic structure. The existence of three distinct GnRH families suggests a new, natural nomenclature for the genes, and in addition, we present a logical proposal for naming the peptide sequences. The two recently discovered GnRH genes are unusual because they encode decapeptides that are identical in all the species in which they have been found. The control of gene expression also differs among the three gene families as might be expected since they have had separate evolutionary trajectories for perhaps 500 million years.

    View details for Web of Science ID 000081689400003

    View details for PubMedID 10433863

  • Second form of gonadotropin-releasing hormone in mouse: immunocytochemistry reveals hippocampal and periventricular distribution FEBS LETTERS Gestrin, E. D., White, R. B., Fernald, R. D. 1999; 448 (2-3): 289-291


    Hypothalamic GnRH (GnRH-I) is known and named for its role in regulating reproductive function in vertebrates by controlling release of gonadotropins from the pituitary. However, another form of GnRH of unknown function (pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly; GnRH-II) is expressed in the mesencephalon of all vertebrate classes except jawless fish. Here we show with immunocytochemical staining that the GnRH-II peptide is localized to the mouse midbrain as in other vertebrates, as well as in cells surrounding the ventricles and in cells adjacent to the hippocampus. Staining of adjacent sections using GnRH-I antibody revealed that the distribution of GnRH-I does not overlap with that of GnRH-II.

    View details for Web of Science ID 000079782900019

    View details for PubMedID 10218494

  • Multifocal lenses compensate for chromatic defocus in vertebrate eyes JOURNAL OF COMPARATIVE PHYSIOLOGY A-NEUROETHOLOGY SENSORY NEURAL AND BEHAVIORAL PHYSIOLOGY Kroger, R. H., Campbell, M. C., Fernald, R. D., Wagner, H. J. 1999; 184 (4): 361-369


    The focal length of the vertebrate eye is a function of wavelength, i.e. the eye suffers from longitudinal chromatic aberration. Chromatic defocus is a particularly severe problem in eyes with high light-gathering ability, since depth of field is small due to a pupillary opening that is large in relation to the focal length of the eye. Calculations show that in such eyes only a narrow spectral band of light can be in focus on the retina. For the major part of the visual spectrum, spatial resolution should be limited by the optics of the eye and far lower than the resolving power achievable by the retinal cone photoreceptor mosaic. To solve this problem, fishes with irises unresponsive to light have developed lenses with multiple focal lengths. Well-focused images are created at the wavelengths of maximum absorbance of all spectral cone types. Multifocal lenses also appear to be present in some terrestrial species. In eyes with mobile irises, multifocal lenses are correlated with pupil shapes that allow all zones of the lens, with different refractive powers, to participate in the imaging process, irrespective of the state of pupil constriction.

    View details for Web of Science ID 000081257700002

    View details for PubMedID 10377973

  • Regional expression of mRNA encoding a second form of gonadotropin-releasing hormone in the macaque brain ENDOCRINOLOGY Urbanski, H. F., White, R. B., Fernald, R. D., Kohama, S. G., Garyfallou, V. T., Densmore, V. S. 1999; 140 (4): 1945-1948


    In mammals, reproduction is thought to be controlled by a single neuropeptide, gonadotropin-releasing hormone (GnRH-I), which regulates the synthesis and secretion of gonadotropins from the pituitary gland. However, another form of this decapeptide (GnRH-II), of unknown function, also exists in the brain of many vertebrate species, including humans; it is encoded by a different gene and its amino acid sequence is 70% identical to that of GnRH-I. Here we report the cloning of a GnRH-II cDNA from the rhesus macaque (Macaca mulatta), and show for the first time by in situ hybridization that GnRH-II mRNA is expressed in the primate midbrain, hippocampus and discrete nuclei of the hypothalamus, including the supraoptic, paraventricular, suprachiasmatic and arcuate. Because the regional distribution pattern of cells containing GnRH-II mRNA is largely dissimilar to that of cells containing GnRH-I mRNA, it is likely that these two cell populations receive distinct neuroendocrine inputs and thus regulate GnRH synthesis and release differently.

    View details for Web of Science ID 000079248200055

    View details for PubMedID 10098535

  • Ontogeny of gonadotropin-releasing hormone (GnRH) gene expression reveals a distinct origin for GnRH-Containing neurons in the midbrain GENERAL AND COMPARATIVE ENDOCRINOLOGY White, R. B., Fernald, R. D. 1998; 112 (3): 322-329


    In the teleost fish, Haplochromis burtoni, three gonadotropin-releasing hormone (GnRH) peptides and their corresponding cDNA sequences and full-length genes have previously been reported. Here we describe the ontogeny of mRNA expression for these three GnRH forms in H. burtoni. Each of the three forms has been shown to have a distinct spatial expression pattern in the adult brain. ¿Ser8¿GnRH (the releasing form) is expressed exclusively in the hypothalamus, ¿His5Trp7Tyr8¿GnRH is expressed in the midbrain mesencephalon, and ¿Trp7Leu8¿GnRH is expressed in the terminal nerve area of the telencephalon. Previous work in other animals has shown that GnRH-containing neurons in the preoptic area arise from the olfactory placode and that these cells migrate into their final positions in the brain during early development. By using molecular probes to identify the cell types expressing distinct GnRH forms, our data are consistent with the migration of both ¿Ser8¿GnRH and ¿Trp7Leu8¿GnRH neurons from the placode to their appropriate adult locations in the brain. In contrast, we show that ¿His5Trp7Tyr8¿GnRH neurons arise from the germinal zone of the third ventricle. By using in situ hybridization with digoxigenin-labeled cRNA probes, ¿His5Trp7Tyr8¿GnRH mRNA was first evident at day 4, ¿Trp7Leu8¿GnRH mRNA at day 8, and ¿Ser8¿GnRH mRNA at day 14. However, by using the reverse-transcriptase polymerase chain reaction (RT-PCR), all three GnRH mRNAs were found in whole embryos at day 4 of the 14 days of embryogenesis. This striking difference may be due to the greater sensitivity of RT-PCR compared with in situ hybridization. Alternatively, it is possible that ¿Ser8¿GnRH and ¿Trp7Leu8¿GnRH are expressed outside the brain during early development and only later inside the brain.

    View details for Web of Science ID 000077627900007

    View details for PubMedID 9843638

  • Cell death precedes rod neurogenesis in embryonic teleost retinal development DEVELOPMENTAL BRAIN RESEARCH Hoke, K. L., Fernald, R. D. 1998; 111 (1): 143-146


    We measured cell death in the retinas of embryonic and adult teleost fish using TUNEL staining. Following a wave of cell birth during embryogenesis that generates all retinal cell types except rods, cell death occurs in all three nuclear layers. The lack of a corresponding pattern of cell death in the growing adult margin suggests different roles for death during embryogenesis and adult neurogenesis.

    View details for Web of Science ID 000076980100015

    View details for PubMedID 9804930

  • Genomic structure and expression sites of three gonadotropin-releasing hormone genes in one species GENERAL AND COMPARATIVE ENDOCRINOLOGY White, R. B., Fernald, R. D. 1998; 112 (1): 17-25


    In the teleost fish, Haplochromis burtoni, gonadotropin-releasing hormone (GnRH) peptide has been localized to three distinct regions in the brain. Each GnRH population is associated with expression of a distinct cDNA as previously described. Here we report the complete genomic sequences encoding these three forms and compare their structural organization, putative regulatory elements, and expression patterns in the body. All three genes share a common structure of four exons: the first exon encodes the 5' untranslated region; the second exon encodes the signal sequence, GnRH decapeptide, and the 5' end of the GnRH-associated peptide (GAP); the third exon consists entirely of GAP coding sequence; and the fourth exon encodes the 3' end of GAP and the 3' untranslated region. Each of the three GnRH genes has been shown previously to have a distinct spatial expression pattern in the brain, and here we use reverse transcription and cDNA amplification to demonstrate that each gene is expressed in the body. The gene encoding the releasing form, ¿Ser8¿GnRH, is expressed in the heart, liver, spleen, kidney, and testis, as well as in the preoptic area. The ¿His5Trp7Tyr8¿GnRH gene is expressed in the testis as well as in the midbrain. The ¿Trp7Leu8¿GnRH gene is expressed in the testis and the terminal nerve area. We examined the 500 bp upstream of exon 1 in all three H. burtoni genes and identified putative binding sites for glucocorticoid receptor, androgen receptor, and progesterone receptor, as well as the transcription factors Ap-1 and Sp-1. The genomic sequence encoding the terminal nerve form of GnRH (i.e., ¿Trp7Leu8¿GnRH) in H. burtoni is remarkably similar to that encoding the presumed releasing form of GnRH in salmonids, especially in the 3' intergenic region. Taken together with phylogenetic and mRNA localization data in salmonids, these data suggest that the gene encoding the releasing form of GnRH in salmonids may not yet be described.

    View details for Web of Science ID 000076260700003

    View details for PubMedID 9748399

  • The olfactory system of a cichlid fish responds to steroidal compounds JOURNAL OF FISH BIOLOGY Robison, R. R., Fernald, R. D., Stacey, N. E. 1998; 53 (1): 226-229
  • The embryogenesis of rod photoreceptors in the teleost fish retina, Haplochromis burtoni DEVELOPMENTAL BRAIN RESEARCH Hagedorn, M., Mack, A. F., Evans, B., Fernald, R. D. 1998; 108 (1-2): 217-227


    Development of the retina, like that of other tissues, occurs via an orderly sequence of cell division and differentiation, producing the functional retina. In teleost fish, however, cell division and differentiation in the retina continue throughout the life of the animal in two distinct ways. Stem cells in a circumferential germinal zone at the periphery of the retina give rise to all retinal cell types and progenitor cells located throughout the retina in the outer nuclear layer (ONL) produce new rod photoreceptors. These processes in adult retina recapitulate in space the embryonic events responsible for forming the retina. Analysis of these events in an African cichlid fish, Haplochromis burtoni, confirmed that cone photoreceptors differentiate first, followed by rod photoreceptors. Correspondingly, at the margin of the eye, cone photoreceptors differentiate nearer to the margin than do rods. Control of photoreceptor production is not understood. Here we present the time of appearance and distribution pattern of GABA and vimentin which are candidates for the control of retinal cell division and differentiation. Antibody staining reveals that both GABA and vimentin exhibit unique patterns of expression during embryonic retinal development. Vimentin immunoreactivity is evident throughout the retina in a spoke-like pattern between developmental Days 4 and 7, as both cone and rod photoreceptors are being formed. GABA is expressed in horizontal cells between Days 5 and 7, corresponding to the onset of rod differentiation in time and in position within the retina. Moreover, the wave of GABAergic staining in the horizontal cells parallels the wave of rod differentiation across the embryonic retina of H. burtoni. Thus, GABA may play a role in the development of rod photoreceptors.

    View details for Web of Science ID 000075154100021

    View details for PubMedID 9693798

  • Second gene for gonadotropin-releasing hormone in humans PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA White, R. B., Eisen, J. A., Kasten, T. L., Fernald, R. D. 1998; 95 (1): 305-309


    Gonadotropin-releasing hormone (GnRH) is a decapeptide widely known for its role in regulating reproduction by serving as a signal from the hypothalamus to pituitary gonadotropes. In addition to hypothalamic GnRH (GnRH-I), a second GnRH form (pGln-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly; GnRH-II) with unknown function has been localized to the midbrain of many vertebrates. We show here that a gene encoding GnRH-II is expressed in humans and is located on chromosome 20p13, distinct from the GnRH-I gene that is on 8p21-p11.2. The GnRH-II genomic and mRNA structures parallel those of GnRH-I. However, in contrast to GnRH-I, GnRH-II is expressed at significantly higher levels outside the brain (up to 30x), particularly in the kidney, bone marrow, and prostate. The widespread expression of GnRH-II suggests it may have multiple functions. Molecular phylogenetic analysis shows that this second gene is likely the result of a duplication before the appearance of vertebrates, and predicts the existence of a third GnRH form in humans and other vertebrates.

    View details for Web of Science ID 000071429500059

    View details for PubMedID 9419371

  • Cell movement and cell cycle dynamics in the retina of the adult teleost Haplochromis burtoni JOURNAL OF COMPARATIVE NEUROLOGY Mack, A. F., Fernald, R. D. 1997; 388 (3): 435-443


    The authors analyzed the pattern of neurogenesis, the time frame of cell movement, and the cell cycle kinetics of a population of stem cells located in the outer nuclear layer in the retina of the adult teleost Haplochromis burtoni. These stem cells continue to give rise to new rod photoreceptors throughout life. The new rods move vitread after the last cell division. The authors investigated events during cell division and cell differentiation by using one marker that labels dividing cells transiently (proliferating cell nuclear antigen) along with another marker that labels dividing cells permanently (bromodeoxyuridine). The bulk of cell movement does not occur within 24 hours after S-phase labeling but is clearly underway 12 hours later, shortly after mitosis. The cell cycle length was estimated to be approximately 25 hours. The distribution of labeled cells at various times after S-phase suggests that new rods are generated by asymmetric cell division, that is, one of the daughter cells moves after mitosis and becomes postmitotic, while the other daughter cell remains in place and reenters the cell cycle. The proliferation patterns across the retina suggest that the location of areas of mitotic activity changes over time. The authors hypothesize that local extracellular factors control the rate of cell division in a given area, thereby keeping the overall rod density constant.

    View details for Web of Science ID A1997YE27700006

    View details for PubMedID 9368851

  • The evolution of eyes Fernald, R. D. KARGER. 1997: 253-259


    Eyes are the preeminent source of sensory information for the brain in most species, and many features of eyes reflect evolutionary solutions to particular selective pressures, both from the nonbiological environment and from other animals. As a result, the evolution of eyes, among all the sense organs, has attracted considerable attention from scientists. Paired eyes in the three major phyla, vertebrates, arthropods and mollusks, have long been considered to be classic examples of evolutionary convergence. At the macroscopic level, this must be true since they arise from different tissues and have evolved radically different solutions to the common problem of collecting and focusing light. However, opsin, the light-absorbing receptor protein, has a significant amount of shared DNA sequence homology across the phyla, and recently it has been discovered that some part of ocular development in different phyla is coordinated by a homologous, gene, Pax-6. So, although eyes from diverse phyla are clearly not homologous, neither can they be viewed as resulting solely from convergence. Instead, this shows that homology at the molecular level of organization does not predict homology at the organ or organismic level. The presence of homologous constituent molecules in nonhomologous structures reminds us that molecules are not eyes.

    View details for Web of Science ID A1997XW61700008

    View details for PubMedID 9310200

  • Stress and dominance in a social fish JOURNAL OF NEUROSCIENCE Fox, H. E., White, S. A., Kao, M. H., Fernald, R. D. 1997; 17 (16): 6463-6469


    Many aspects of reproductive physiology are subject to regulation by social interactions. These include changes in neural and physiological substrates of reproduction. How can social behavior produce such changes? In experiments reported here, we manipulated the social settings of teleost fish and measured the effect (1) on stress response as reflected in cortisol production, (2) on reproductive potential as measured in production of the signaling peptide, gonadotropin-releasing hormone, and (3) on reproductive function measured in gonad size. Our results reveal that the level of the stress hormone cortisol depends critically on both the social and reproductive status of an individual fish and on the stability of its social situation. Moreover, the reproductive capacity of an individual fish depends on these same variables. These results show that social encounters within particular social contexts have a profound effect on the stress levels as well as on reproductive competence. Social behavior may lead to changes in reproductive state through integration of cortisol changes in time. Thus, information available from the stress pathway may provide socially relevant signals to produce neural change.

    View details for Web of Science ID A1997XU78100042

    View details for PubMedID 9236253

  • Effect of social rank on brain monoaminergic activity in a cichlid fish BRAIN BEHAVIOR AND EVOLUTION Winberg, S., WINBERG, Y., Fernald, R. D. 1997; 49 (4): 230-236


    In Haplochromis burtoni, an African cichlid fish, male sexual maturation is regulated via social interactions, and these effects are mediated by gonadotropin-releasing-hormone (GnRH)-containing neurons in the preoptic area of the brain. Since brain monoaminergic systems are known to be involved in the regulation of GnRH release, and the activity of these systems is influenced by agonistic interactions, we analyzed the effect of social status on brain monoaminergic activity in H. burtoni. Animals were either (1) in normal social groups consisting of two males and four females or (2) in groups of one male and five females. Quantitative behavioral observations were made on each group of animals and, following sacrifice several physiological measurements were made. Concentrations of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA, the main 5-HT metabolite) and tryptophan (TRP, the amino acid precursor of 5-HT), dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC, the main DA metabolite) were measured. The 5-HIAA/5-HT and DOPAC/DA ratios were calculated and used as indexes of 5-HT and DA activity, respectively. In addition, the gonadosomatic index was calculated from body and gonadal weights and used as an index of reproductive status. Concentrations of 5-HIAA as well as 5-HIAA/5-HT ratios were significantly higher in the brainstem of non-territorial males than in that of territorial males, and similar trends were seen in the telencephalon and hypothalamus. Moreover, TRP concentrations in the telencephalon and brainstem were significantly lower in non-territorial males. In this species, sexual maturation in females is not socially regulated, and there was no significant correlation between measured antagonistic behavior and biochemical indices. These results suggest a fundamental difference in the neurochemical responses between male and female H. burtoni.

    View details for Web of Science ID A1997WP22100003

    View details for PubMedID 9096910

  • Changing through doing: Behavioral influences on the brain RECENT PROGRESS IN HORMONE RESEARCH, PROCEEDINGS OF THE 1996 CONFERENCE, VOL 52 White, S. A., Fernald, R. D. 1997; 52: 455-474


    It seems self-evident that the brain controls behavior but does behavior also "control" the brain? This chapter examines evidence that behavior can and does influence specific aspects of brain structure and function. Evidence for such influence is easily obtained on an evolutionary time scale, since the selective forces found in the ecological niche of the animal are typically reflected in its sensory and motor activities as well as its body shape and behavioral habits. Similarly, during development, there is ample evidence that the behavior acts in concert with the environment to establish structural changes in the brain that last a lifetime. Perhaps most surprisingly there is now evidence that social behavior can cause changes in the brain in adult animals and that these changes are reversible. The changes caused by behavioral interactions can be dramatic and typically are related to reproductive behavior. Understanding the mechanisms responsible for dynamic changes in the nervous systems of adult animals is a major challenge and the discovery that it can occur may lead to insights about other systems where behavior sculpts the brain.

    View details for Web of Science ID 000071740900018

    View details for PubMedID 9238863

  • Rod photoreceptor neurogenesis PROGRESS IN RETINAL AND EYE RESEARCH Hoke, K. L., Fernald, R. D. 1997; 16 (1): 31-49
  • Characterization of two new preproGnRH mRNAs in the tree shrew: First direct evidence for mesencephalic GnRH gene expression in a placental mammal GENERAL AND COMPARATIVE ENDOCRINOLOGY Kasten, T. L., White, S. A., Norton, T. T., Bond, C. T., Adelman, J. P., Fernald, R. D. 1996; 104 (1): 7-19


    Reproductive maturation and regulation is centrally orchestrated by gonadotropin-releasing hormone (GnRH). GnRH produced in the vertebrate hypothalamus acts on the pituitary to regulate gonadotropins. In nonplacental mammalian species, it has recently been shown that a second GnRH gene is expressed in mesencephalic cells. Here, we report the cDNA sequences and expression patterns for two distinct genes encoding the hypothalamic and mesencephalic GnRH forms in the brain of a placental mammal, the tree shrew (Tupaia glis belangeri). The novel mammalian GnRH form, designated here as [His5Trp7Tyr8]GnRH (often called chicken GnRH II), is expressed in neurons of the mesencephalon and is the first nonhypothalamic form to be isolated from a mammal. Its peptide sequence is identical to the form previously reported in fish, amphibians, reptiles, and birds, revealing that it has remained unchanged for 500 million years. In contrast, the sequences of the hypothalamic GnRH decapeptides vary by as much as 50% across vertebrate species. The remarkable sequence conservation of mesencephalic GnRH suggests that it has been highly constrained throughout evolution, perhaps indicating an important, conserved nongonadotropic role. The discovery and localization of two mRNAs encoding distinct GnRH forms in an advanced mammal suggest that other mammals, including primates, may also have a second GnRH gene with expression localized in the midbrain.

    View details for Web of Science ID A1996VL24200002

    View details for PubMedID 8921350

  • Androgen regulation of hypothalamic neurons containing gonadotropin-releasing hormone in a cichlid fish: Integration with social cues HORMONES AND BEHAVIOR Soma, K. K., Francis, R. C., Wingfield, J. C., Fernald, R. D. 1996; 30 (3): 216-226


    Reproduction in vertebrates is regulated by internal signals such as hormone levels and by external signals such as social interactions. In an African cichlid fish, Haplochromis burtoni, the effect of social interactions is evident in the hypothalamo-pituitary-gonadal (HPG) axis of males. Territorial males, characterized by aggressive and reproductive activity, have significantly larger hypothalamic gonadotropin-releasing hormone (GnRH)-containing neurons and larger testes than nonterritorial males. Furthermore, a switch in the social status of an adult male causes a corresponding change in GnRH neuron size and testis size. Here we show that the GnRH-containing neurons in the hypothalamus of adult territorial males are also influenced by gonadal hormones. Castration of territorial males caused GnRH neurons to increase in size. This neuronal hypertrophy in castrated animals was prevented either by testosterone (T) or 11-ketotestosterone (KT) treatment. Estradiol (E2) treatment did not reduce GnRH cell size in castrated animals. These results suggest that androgens reduce the size of GnRH cells through negative feedback. Since E2 had no effect, androgen influence on GnRH cell size appears to be independent of aromatization. These data are consistent with the hypothesis that the setpoint for hypothalamic GnRH cell size is determined by social cues and that this setpoint is maintained by negative feedback from gonadal androgens.

    View details for Web of Science ID A1996VN86200003

    View details for PubMedID 8918677

  • Nonuniform distribution of cell proliferation in the adult teleost retina BRAIN RESEARCH Kwan, J. W., Lee, M. J., Mack, A. F., Chiu, J. F., Fernald, R. D. 1996; 712 (1): 40-44


    Teleost fish continue to grow throughout life, and their eyes enlarge correspondingly. Within the eye, the retina grows by stretching existing tissue and adding new cells. Cell addition occurs in two ways: First, all cell types except rod photoreceptors are added circumferentially at the edge of the eye where the retina meets the iris; second, rod photoreceptors are generated from a population of rod progenitor cells which divide throughout the outer nuclear layer (ONL). To determine the spatial distribution of rod progenitor cells across the teleost retina, we labeled dividing cells with an antibody to proliferating cell nuclear antigen (PCNA) throughout a 24 h period. We found a significantly higher density of dividing rod precursor cells at the nasal and temporal margins than in the central retina throughout the 24 h cycle. At night, the density of dividing cells is significantly greater at the nasal pole of the eye. The difference between cell division at the center and the margin was reduced at night when the density of cell division in the central retina increased significantly. Taken together, these data suggest that the eye grows asymmetrically, with more cells added at the nasal pole. Possible developmental causes and functional consequences of the reported distribution of cell divisions in time and location are presented.

    View details for Web of Science ID A1996UC68800005

    View details for PubMedID 8705305

  • The population of GnRH-containing neurons showing socially mediated size changes project to the pituitary in a teleost, Haplochromis burtoni BRAIN BEHAVIOR AND EVOLUTION Bushnik, T. L., Fernald, R. D. 1995; 46 (6): 371-377


    Reproductive function in all vertebrates is controlled by the brain-pituitary-gonadal axis. In teleost fish, endocrine cells within the adenohypophysis are grouped together and each collection of cells is innervated by specific neuropeptide fibers. An important regulatory step in reproductive control is gonadotropin-releasing hormone (GnRH), whose delivery to the pituitary is responsible for its release of gonadotropins. The hormone GnRH has been shown to play a critical role in the social control of reproduction in a teleost fish, Haplochromis burtoni. However, there has been no direct evidence that the preoptic area GnRH neurons project to the pituitary. In this study, we used a retrograde tracer and immunohistochemistry to identify those GnRH containing neurons that project to the adenohypophysis. We compared reproductively active territorial males with quiescent non-territorial males to discover whether the connectivity of the preoptic area GnRH neurons depends on the reproductive status of the male. We found that, irrespective of reproductive status, most GnRH neurons in the preoptic area project to the pituitary and that all of these GnRH neurons show the soma size change that has been associated with reproductive status in Haplochromis burtoni. Based on these data, we propose that there is a single population of GnRH containing cells in the preoptic area that change size as a function of reproductive state and that this entire population projects to the pituitary. This is the first direct demonstration that this essential circuit, linking GnRH neurons in the preoptic area to the pituitary, exists.

    View details for Web of Science ID A1995TL29000004

    View details for PubMedID 8719758

  • A novel, rapid flat-mounting technique for visualizing antibody labeling in the retina JOURNAL OF NEUROSCIENCE METHODS Colbert, S. H., Mack, A. F., Fernald, R. D. 1995; 62 (1-2): 179-183


    Complete analysis of retinal tissue is difficult because it consists of a thin neural tissue spread across the back of a hemispheric surface. Conventional sectioning in a plane parallel to a central axis of symmetry produces a large number of samples, each containing only a small amount of the tissue of interest. Consequently, quantitative comparison of any feature of interest typically uses a small fraction of the sections from each retina, because analysis of the entire collection of sections is too time consuming. Such a sampling process can lead to misleading or erroneous conclusions. We present a new method which allows complete analysis of the retina using a small number of samples produced by sectioning flattened retinas. This procedure is straightforward as illustrated using an antibody against proliferating cell nuclear antigen (PCNA) to locate dividing cells in the teleost fish retina. Immunocytochemical staining on flat-sectioned retinas was quantified using a computer-based image analysis system. When the cells of interest are randomly distributed, conventional sampling procedures can seriously under- or over-estimate their number. The new technique presented allows significantly more efficient examination and quantification of the entire retina as compared to conventional techniques.

    View details for Web of Science ID A1995TL54900024

    View details for PubMedID 8750101



    Gonadotropin-releasing hormone (GnRH) is known and named for its essential role in vertebrate reproduction. Release of this decapeptide from neurons in the hypothalamus controls pituitary gonadotropin levels which, in turn, regulate gonadal state. The importance of GnRH is underscored by its widespread expression and conservation across vertebrate taxa: five amino acids are invariant in all nine known forms, whereas two others show only conservative changes. In most eutherian mammals, only one form, expressed in the hypothalamus, is thought to exist, although in a recent report, antibody staining in developing primates suggests an additional form. In contrast, multiple GnRH forms and expression loci have been reported in many non-mammalian vertebrates. However, evidence based on immunological discrimination does not always agree with analysis of gene expression, since GnRH forms encoded by different genes may not be reliably distinguished by antibodies. Here we report the expression of three distinct GnRH genes in a teleost fish brain, including the sequence encoding a novel GnRH preprohormone. Using in situ hybridization, we show that this form is found only in neurons that project to the pituitary and exhibit changes in soma size depending on social and reproductive state. The other two GnRH genes are expressed in other, distinct cell populations. All three genes share the motif of encoding a polypeptide consisting of GnRH and a GnRH-associated peptide. Whereas the GnRH moiety is highly conserved, the GnRH-associated peptides are not, reflecting differential selective pressure on different parts of the gene. GnRH forms expressed in nonhypothalamic regions may serve to coordinate reproductive activities of the animal.

    View details for Web of Science ID A1995RR84400057

    View details for PubMedID 7667296



    To understand the cellular context of neuronal differentiation in the vertebrate retina, we analyzed the behavior of a class of progenitor cells in the outer nuclear layer of the teleost retina which divide throughout the animal's life and generate only rod photoreceptors. We present evidence that these progenitors reside adjacent to the outer limiting membrane of the retina during all phases of cell cycle. After final cell division, postmitotic cells move inward, toward the vitreal boundary of the outer nuclear layer, before they give rise to new rods. This movement is remarkable because it occurs in the mature, functioning retina. We hypothesize that only one of the two progenitor daughter cells moves while the other remains adjacent to the outer limiting membrane to divide again.

    View details for Web of Science ID A1995RH86300013

    View details for PubMedID 7601304

  • PRIMARY STRUCTURE OF SOLITARY FORM OF GONADOTROPIN-RELEASING-HORMONE (GNRH) IN CICHLID PITUITARY - 3 FORMS OF GNRH IN BRAIN OF CICHLID AND PUMPKINSEED FISH REGULATORY PEPTIDES Powell, J. F., Fischer, W. H., Park, M., Craig, A. G., Rivier, J. E., White, S. A., Francis, R. C., Fernald, R. D., Licht, P., Warby, C., Sherwood, N. M. 1995; 57 (1): 43-53


    GnRH is a decapeptide family with at least nine distinct structures. Vertebrates, except for most placental mammals, have more than one of these GnRH forms within the brain. We report chromatographical and immunological evidence that three forms of GnRH are in the brains of both cichlid (Haplochromis burtoni) and pumpkinseed (Lepomis gibbosus) fishes. We argue that the three forms correspond to those previously described as sea bream GnRH (sbGnRH), chicken GnRH-II and salmon GnRH. In contrast, only one GnRH form was present in the pituitary of the cichlid and is identified as sbGnRH by amino acid sequence. This is the first report in which the primary structure of GnRH is determined from pituitary tissue. The N-terminus was identified by monitoring the digestion of the peptide by pyroglutamate aminopeptidase with matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS). The amidation of the C-terminus was established using an esterification procedure for monitoring with MALDI-MS. This report supports the idea that three forms of GnRH within one species is widespread in the order Perciformes. The present study establishes sbGnRH as the third GnRH form in H. burtoni and predicts that sbGnRH is synthesized in preoptic neurons, then transported to the pituitary in the preoptic-hypophyseal axons for the release of one or both gonadotropins.

    View details for Web of Science ID A1995QY48000003

    View details for PubMedID 7644702



    Teleost fish retinas continue to add neurons throughout life, and evidence from in vitro experiments have implicated insulin-like growth factors (IGFs) in this process. To discover whether these factors are expressed in vivo, we have examined their expression in the cichlid fish, Haplochromis burtoni. Three lines of evidence show that IGFs are present in the fish retina. An IGF-I specific antibody, sm 1.2, binds preferentially to the retinal outer plexiform layer, in areas of cone photoreceptor synaptic endings. Northern blots of mRNA hybridized with riboprobes from trout IGF-I and IGF-II genes revealed transcripts of approximately 6.5 and 4.9 kb, respectively. The IGF-I probe detected an additional transcript of 1.2 kb in liver but not in retinal mRNA. In situ hybridization with digoxigenin-labeled riboprobes revealed that the IGF gene product is localized in the cone photoreceptors. These results show that cone photoreceptors are the source of IGFs in the fish retina, consistent with the hypothesis that IGFs play a role in regulating production of new neurons in the teleost retina.

    View details for Web of Science ID A1995QW76200005

    View details for PubMedID 7654603



    To determine whether the number of cell divisions in the teleost retina exhibited a regular daily variation, we labeled dividing cells with an antibody to proliferating cell nuclear antigen. The number of dividing rod precursor cells in the outer nuclear layer of the retina were counted in retinas from the telost fish Haplochromis burtoni, sacrificed at 4-h intervals during a standard light-dark cycle and in constant darkness. These rod precursor cells exhibited a striking rhythm of cell division. The highest number of cell divisions (acrophase) was found to occur at night when it was approximately 3 times higher than during the day. The observed rhythm persisted in animals held in constant darkness. We suggest that this endogenous 24-h rhythm of rod precursor cell division may be controlled by a circadian clock. Although there are several examples of continuously proliferating cell populations which exhibit circadian or diurnal rhythms, this appears to be the first documentation of a rhythm of division in cells destined to become neurons.

    View details for Web of Science ID A1995QJ68200015

    View details for PubMedID 7757463

  • Social control of cell size: Males and females are different GENE EXPRESSION IN THE CENTRAL NERVOUS SYSTEM Fernald, R. D. 1995; 105: 171-177


    Successful animals survive because they modify their behavior in response to changes in their physical and social environments. Some responses such as fleeing or fighting, are immediate and can be understood or at least described by their proximate causes. Other modifications occur in animals over a longer time frame because they require tissue growth (or loss), changes in responsiveness to signalling molecules, or other alterations in the regulation of physiological systems. There are numerous examples of the short-term cause-effect relationships which are known in some detail. In contrast, less is known about how long-term changes result from environmental or social signals. Since reproduction is arguably the single most important aspect of an animal's life, reproductive behaviors offer a unique chance to study such change. Reproduction requires exquisite coordination of physiological state and behavioral acts. Many aspects of reproductive behavior occur only under natural conditions so it is imperative to analyze naturally occurring behaviors in real animals, preferably in the natural habitat. We have been studying an African cichlid fish in natural and semi-natural conditions because the connection between physiology and behavior can be easily seen. Moreover, the consequence of social success can be traced directly to changes in the brain, both in the short and long term. In this species, territorial males inhibit sexual maturation of nonterritorial males during development. Even after a male becomes sexually mature and territorial, being defeated causes his gonads to regress rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)

    View details for Web of Science ID A1995BE39G00014

    View details for PubMedID 7568874



    Fish were reared in 6 conditions: broad spectrum white light, total darkness, scotopic illumination, and 3 monochromatic colors matched to the absorption spectra of the three cone types to study the influence of the light regime on the regulation of eye growth in the African cichlid fish Haplochromis burtoni. Fish reared in total darkness showed high variability in naso-temporal diameter and axial length of the eye. Animals reared in darkness and in scotopic illumination had significantly larger eyes relative to lens size in comparison to fish reared in white light. Eye size and shape was nearly identical in fish reared in monochromatic and in white light. Because of overlap in the absorption spectra of the three cone types of H. burtoni it could not be resolved whether the regulatory mechanism receives input from all three cone types or only from the green (523 nm) sensitive cones. It is clear from our results, however, that neither the blue (455 nm) nor the yellow sensitive (562 nm) cones alone are responsible for eye size regulation. It seems equally unlikely that all three cone types have to act in concert for normal growth of the eye.

    View details for Web of Science ID A1994NZ96400002

    View details for PubMedID 7941383



    Refractive index distribution in the teleost crystalline lens was measured with a nondestructive method in freshly excised lenses of the African teleost fish Haplochromis burtoni. Independently, spherical aberration was measured in a parallel set of lenses. The measured refractive index profiles show a continual decrease of refractive index from the center to the surface of the lens. The H. burtoni lens is of high optical quality and slightly overcorrected for spherical aberration. Details of the small residual spherical aberration were accurately predicted by ray-tracing model calculations based on the measured refractive index profile. The refractive index profile and the spherical aberration both show more complex characteristics than suggested by earlier measurements and lens models.

    View details for Web of Science ID A1994NZ96400003

    View details for PubMedID 7941384



    We investigated changes in two gonadotropin releasing hormone (GnRH)-containing neuronal populations during juvenile development in the African teleost, Haplochromis burtoni. Juveniles were sampled at weekly intervals and GnRHir neurons were identified through immunocytochemistry (ICC), then counted and measured on computer-captured video images. Soma size of GnRH neurons in the preoptic area (POA), which regulate gonadotropin release from the pituitary, is socially modulated in adults. Here we show that in juveniles the soma size of these neurons increases as a linear function of body weight. Terminal nerve (TN) GnRHir neurons, in contrast, are not involved in pituitary regulation and their soma size is not socially modulated in adults. In juveniles, soma size of these neurons is a quadratic function of body size and the covariance of soma size and body size is much less than in the POA GnRHir neurons. In both populations, GnRHir neuronal number covaries with body size or age only in the earliest juvenile stages. Analysis of the development of these two distinct GnRHir neuronal populations provides insight into their functional differentiation in adults.

    View details for Web of Science ID A1994NH41400001

    View details for PubMedID 8026070



    In vertebrates, the gonadotropin-releasing hormone (GnRH) decapeptide is secreted from hypothalamic nerve terminals to regulate reproduction via control of synthesis and release of pituitary gonadotropins. Only one GnRH peptide has been found in mammals, with one exception, although numerous other vertebrate species express more than one of the eight known decapeptide forms as shown by immunocytochemical labeling of distinct cell groups in the brain. However, neither the functional nor the evolutionary relationships among these GnRH forms are clear, because only one preprohormone gene sequence from any species has been reported. The most ubiquitous alternative form of GnRH is [His5,Trp7,Tyr8]GnRH (also referred to as chicken-II), which differs from the mammalian sequence at amino acids 5, 7, and 8. This peptide has been shown to have the most potent releasing-hormone activity, although immunocytochemical staining has suggested it is synthesized only in the mesencephalon. Here we report the cloning and expression pattern of the gene for the precursor of this form from the teleost fish Haplochromis burtoni. This is the second GnRH-encoding gene to be characterized in this species. The newly discovered preprohormone gene differs from that previously reported in two ways. First, whereas the original gene predicts only a single associated peptide, this one predicts two associated peptides, both of which appear to be unique. Second, the gene for [His5,Trp7,Tyr8]GnRH is expressed in only one cell group in the mesencephalon. In contrast, the previously reported gene is expressed only in the terminal nerve. The striking differences between the preprohormone structure and localization suggest that the genes coding for the two known GnRH forms in H. burtoni did not arise from a recent duplication event. Interestingly, neither of the two genes found to date in this species is expressed in cells which project from the hypothalamus to the pituitary, suggesting that yet a third gene coding for GnRH may exist.

    View details for Web of Science ID A1994MX21000049

    View details for PubMedID 8108425



    We tested the effects of several growth factors on the proliferation and differentiation of cells in the teleost retina which typically become rod photoreceptors to understand their regulation. Using organotypic slice cultures of differentiated teleost fish retinal tissue, we found that insulin and insulin-like growth factor I (IGF-I) stimulate proliferation of rod precursor cells whereas basic fibroblast growth factor (bFGF) does not. In the presence of bFGF, however, a greater proportion of the cells that had divided expressed a rod photoreceptor-specific phenotype than did control slices. This suggests insulin and the related IGF-I can influence the regulation of neuronal cell division whereas bFGF promotes the differentiation of neuronal stem cells into rod photoreceptors in retinal slice culture. These results support the idea that cell division and differentiation are differentially regulated and diffusible factors play a role in this process.

    View details for Web of Science ID A1993MQ54200004

    View details for PubMedID 8149584



    Winter flounder (Pseudopleuronectes americanus) are hatched as bilaterally symmetric larvae which live near the ocean surface. At metamorphosis, they become laterally compressed, one eye migrates to the opposite side of the head, and they live the remainder of their lives lying on their blind side on the ocean floor. The present study characterizes and quantifies retinal cell distribution throughout the larval period and contrasts it with the adult retina. Based on light- and electron-microscopic analyses, retinas of larval flounder contain only a single cone-like photoreceptor type, arranged in a hexagonal array. In contrast, after metamorphosis, the adult retina has three types of photoreceptors: rods, single cones, and double cones. Rod photoreceptors are numerous in the ventral retina and decrease in density dorsad. The cone photoreceptor density, in contrast to rods, is higher in the dorsal retina decreasing ventrad. Adult cone photoreceptors are arranged in a square mosaic with four double cones surrounding one single cone. The differences in larval and adult retinal morphology reflect the distinctly different habitat each occupies.

    View details for Web of Science ID A1993MD85800009

    View details for PubMedID 8257662



    The habitat occupied by larval winter flounder (Pseudopleuronectes americanus) differs considerably in light regime from that of the adult. To understand how the visual system has adapted to such changes, photoreceptor spectral absorbance was measured microspectrophotometrically in premetamorphic and postmetamorphic specimens of winter flounder. Before metamorphosis, larval flounder retinas contain only one kind of photoreceptor which is morphologically cone-like with peak absorbance at 519 nm. After metamorphosis, the adult retina has three types of photoreceptors: single cones, double cones, and rods. The visual pigment in single cones has a peak absorbance at lambda max = 457 nm, the double cones at lambda max = 531 and 547 nm, and the rod photoreceptors at lambda max = 506 nm. Double cones were morphologically identical, but the two members contained either different (531/547 nm) or identical pigments (531/531 nm). The latter type were found only in the dorsal retina. The measured spectral half-bandwidths (HBW) were typical of visual pigments with chromophores derived from vitamin A1 with the possible exception of the long-wavelength absorbing pigment in double cones which appeared slightly broader. Because the premetamorphic pigment absorbance has a different lambda max than those of the postmetamorphic pigments, different opsin genes must be expressed before and after metamorphosis.

    View details for Web of Science ID A1993MD85800010

    View details for PubMedID 8257663



    Reproduction in vertebrates is regulated by the hypothalamic-pituitary-gonadal axis via neural and hormonal feedback. This axis is also subject to exogenous influences, particularly social signals. In the African cichlid fish Haplochromis burtoni, gonadal development in males is socially regulated. A small fraction of the males, which are brightly colored, maintain territories and aggressively dominate inconspicuously colored nonterritorial males. Here we show through manipulation of the social and endocrine environment that changes in social status and gonadal state are accompanied by soma size changes in a population of gonadotropin-releasing hormone-containing neurons in the ventral forebrain. In territorial males, these cells are significantly larger than in nonterritorial males. When an animal switches from being territorial to nonterritorial through a change in social situation, these cells shrink; in animals that change from nonterritorial to territorial status, the cells enlarge. These gonadotropin-releasing hormone-containing cells project to the pituitary and are ultimately responsible for regulating gonadal growth. This mechanism of socially induced cell size change provides the potential for relatively quick adaptive changes in the neuron-endocrine system without nerve cell addition or death. Since the structure of this regulatory axis is conserved among all vertebrates, other species with socially modulated reproductive physiology may exhibit a similar form of physiological regulation.

    View details for Web of Science ID A1993LT43700078

    View details for PubMedID 8356086



    In the preoptico-hypothalamic area (POA) of teleost fish, neurons containing gonadotropin-releasing hormone (GnRH) regulate reproduction through direct projections to pituitary gonadotropes. Here we show that these GnRH-containing cells change size depending on the reproductive and maturational state in female Haplochromis burtoni. We selected animals prior to, during, and after the reproductive portion of their life history, in both brooding and spawning states. Immunocytochemical staining of GnRH-containing neurons in the POA revealed that these cells are up to twice as large in females that have never spawned or are in the act of spawning than they are in females that are carrying broods. Older, postreproductive females have the largest cell sizes. Previous work on male H. burtoni has shown that soma sizes of the homologous neurons change according to social status, with dominant fish having larger cells than subordinates. Since reproductively active females have no apparent social hierarchy and are all exposed to approximately the same external stimuli, the primary factor(s) controlling GnRH-immunoreactive (irGnRH) neuron size appears to be internal reproductive state. Thus, while irGnRH neurons are pleiomorphic in both males and females, cell size change is differently regulated in each.

    View details for Web of Science ID A1993KL12300003

    View details for PubMedID 8426222



    In the African cichlid fish, Haplochromis burtoni, males are either territorial or nonterritorial. Territorial males suppress reproductive function in the nonterritorial males, and have larger gonads and larger gonadotropin-releasing hormone- (GnRH) containing neurons in the preoptic area (POA). We describe an experiment designed to establish the causal relationship between large GnRH neurons and large testes in these males by determining the feedback effects of gonadal sex steroids on the GnRH neurons. Territorial males were either castrated or sham-operated, 4 weeks after which they were sacrificed. Circulating steroid levels were measured, and the GnRH-containing neurons were visualized by staining sagittal sections of the brains with an antibody to salmon GnRH. The soma areas of antibody-stained neurons were measured with a computer-aided imaging system. Completely castrated males had markedly reduced levels of circulating sex steroids [11-ketotestosterone (11KT) and testosterone (T)], as well as 17 beta-estradiol (E2). POA GnRH neurons in castrates showed a significant increase in mean soma size relative to the intact territorial males. Hence, in mature animals, gonadal steroids act as a brake on the growth of GnRH-containing neurons, and gonadal products are not responsible for the large GnRH neurons characteristic of territorial males.

    View details for Web of Science ID A1992JV88100011

    View details for PubMedID 1460466



    Neurogenesis of the developing embryonic retina is described for the African cichlid fish, Haplochromis burtoni, from 4 days post fertilization until all cell phenotypes are generated (day 7). Cell addition and differentiation both begin at the same absolute location which later becomes the central retina. As observed in most other vertebrates, cones and ganglion cells differentiate first, followed by amacrine and bipolar cells. Rod photoreceptors, which are added late, differentiate last. Changes in retinal thickness, retinal stretching, cell size, and cell density were measured during development. From day 4 through 7, there is an increase in retinal thickness largely due to the expansion of the inner plexiform layer (IPL) and outer nuclear layer (ONL). The inner nuclear layer (INL) decreases in thickness and there is a transient decrease in the density of cells in the scleral portion of the INL. Cells increase in size in the ganglion cell layer (GCL) and the vitread INL, decrease in size in the sclerad INL, and remain the same in the ONL. Changes in the density of the cell layers were observed: the density of ONL cells increased, the density of GCL cells decreased, and INL cells increased then decreased. From day 4 to day 6, eye growth is entirely due to cell addition because no retinal stretching was observed in the ONL or the horizontal layer. During this same developmental period, the pattern and rate of neurogenesis were measured in the differentiated portion of the retina by means of 3H-thymidine labeling. A small number of cell divisions within the differentiated INL precede the onset of cell divisions in the ONL. The number of 3H-thymidine labeled cells within the INL increases at a low rate consistent with an asymmetric pattern of cell division characteristic of stem cells. In contrast, cell divisions in the ONL increase exponentially, consistent with a symmetric pattern of cell division characteristic of progenitor cells. Double-label experiments (3H-thymidine and a rod specific opsin antibody) show that some of the symmetrically dividing cells in the ONL express the rod specific opsin within 2 days, suggesting that these dividing cells are rod progenitors. Although we do not hae conclusive evidence, these developmental processes support the hypothesis that stem cells within the INL could be the source of rod precursors in the embryonic teleost retina.

    View details for Web of Science ID A1992JB30400002

    View details for PubMedID 1380013


    View details for Web of Science ID A1992HF92100001

    View details for PubMedID 1575438



    Regeneration of vertebrate sensory cells can be seen as an extension and elaboration of the process of cellular repair and to understand repair requires knowledge of how cell division and cell fate are determined. To approach these problems, we have developed a slice culture for the teleost retina. Cells continue to divide in the same pattern in this slice culture as they do in vivo as demonstrated with [3H]thymidine labeling. Moreover, cells which divided in culture became retinal cell phenotypes as identified with monoclonal antibodies. Some presumptive rod progenitors in the outer nuclear layer in the center of the retina were also labeled cone-specific, possibly as a regeneration response. These data add to the evidence that cell fate is determined by the environment. This slice preparation will be a useful model system for analyzing putative environmental cues responsible for guiding cell proliferation and differentiation in the fish retina.

    View details for Web of Science ID A1992GX80400014

    View details for PubMedID 1728575



    Reproductive maturity among male African cichlids Haplochromis burtoni is cued by a series of environmental and social interactions and is mediated physiologically by GnRH. A cDNA clone encoding the precursor for GnRH was isolated from this teleost. The molecular architecture of the predicted prohormone is analogous to that of the previously characterized mammalian forms; however, the predicted sequence of the associated peptide is strikingly different. Attempts to isolate a putative second precursor using low stringency hybridization were not successful despite evidence that a second related decapeptide exists in at least some teleost species.

    View details for Web of Science ID A1991FX71500007

    View details for PubMedID 1944299



    Thin slices of differentiated fish retinas were maintained up to 5 days in culture conditions where they exhibited properties essentially identical to those found in retinas of intact animals. Retinal slices were prepared by embedding eyecups from young fish in agarose and sectioning them on a vibratome. Phenotypic integrity of specific cell types was maintained, as demonstrated by specific antibody staining patterns. Stem cells in the retinal margin and presumptive rod progenitor cells in the outer nuclear layer continued to proliferate in vitro, just as they do in vivo. Some of these cells differentiated in vitro as demonstrated by labelling both cell division and cell phenotype. After several days in culture, some regeneration-like responses were observed, such as growth of neurites and swelling of cell bodies in the ganglion cell layer. This retinal slice preparation appears to offer a unique opportunity for studying the interactions among developing retinal cells.

    View details for Web of Science ID A1991FC81600009

    View details for PubMedID 2062114

  • REGENERATION OF VERTEBRATE SENSORY RECEPTOR-CELLS - FINAL GENERAL DISCUSSION SYMP ON REGENERATION OF VERTEBRATE SENSORY RECEPTOR CELLS Rubel, E. W., Watt, F. M., Potten, C. S., Farbman, A. I., Lewis, J., Calof, A. L., Margolis, F. L., REH, J. A., Raymond, P. A., Corwin, J. T., Presson, J. C., Fernald, R. D., Steinberg, R. H., Cotanche, D. A., REASNER, D. A., Oakley, B., Ryals, B. M. JOHN WILEY & SONS LTD. 1991: 314–329
  • REGENERATION OF VERTEBRATE SENSORY RECEPTOR-CELLS - FINAL GENERAL DISCUSSION CIBA FOUNDATION SYMPOSIA Rubel, E. W., Watt, F. M., Potten, C. S., Farbman, A. I., Lewis, J., Calof, A. L., Margolis, F. L., REH, J. A., Raymond, P. A., Corwin, J. T., Presson, J. C., Fernald, R. D., Steinberg, R. H., Cotanche, D. A., REASNER, D. A., Oakley, B., Ryals, B. M. 1991; 160: 314-329
  • SOCIAL-CONTROL OF NEURONAL SOMA SIZE JOURNAL OF NEUROBIOLOGY Davis, M. R., Fernald, R. D. 1990; 21 (8): 1180-1188


    Factors responsible for sexual maturation differ significantly among vertebrate species. In many, age is most important, whereas in others seasonal or social cues play a central role. Here we report that maturation in the African cichlid fish Haplochromis burtoni is socially controlled, and that this control includes regulation of soma growth in a population of preoptic neurons immunoreactive to gonadotropin-releasing hormone (irGnRH). Males reared in aquaria among fish of the same age mature sexually in about 3 months, whereas males reared in the presence of older, more aggressive conspecifics remain immature even at 5 months of age. Immature males display hypogonadism and have conspicuously undersized preoptic irGnRH neurons in comparison to those of mature siblings of the same age. This variable maturation rate increases the likelihood that individual males will survive to an age when they can successfully reproduce.

    View details for Web of Science ID A1990EM11900003

    View details for PubMedID 2273399

  • METAMORPHOSIS AND FISH VISION JOURNAL OF NEUROBIOLOGY Evans, B. I., Fernald, R. D. 1990; 21 (7): 1037-1052


    Many species of fish exhibit metamorphosis in which dramatic external transformations occur as a consequence of coordinated changes in gene expression within an organism. Because postembryonic development and change appears to be the rule rather than the exception in teleost fish species, we view metamorphosis as one of many developmental strategies in fish which have continued plasticity as a common theme. Metamorphic changes are manifested in the visual system by modification of photoreceptor peak sensitivity, rod photoreceptor cell addition, and retinal reorganization. These changes correspond to significant changes in the natural habitat of the animal and in its visual capabilities as demonstrated behaviorally. Thyroxine is the main metamorphic hormone as has also been found in amphibia. The sequence of metamorphic events occur in all teleosts, but they are compressed in time in direct developing animals suggesting that such animals might prove useful for understanding the evolution of metamorphosis in fish. It seems likely that rod photoreceptors may have evolved in conjunction with the change from larval to juvenile stage through metamorphosis in indirect developing fishes. During evolution, the contraction and/or loss of the larval stage has resulted in earlier appearance of rod photoreceptors during development although they always arise later than cone photoreceptors. This ontogenetic developmental sequence supports Walls's (1942) proposal that cones are phylogenetically older than rods and suggests that rods may have evolved several times.

    View details for Web of Science ID A1990EF31900008

    View details for PubMedID 2258720



    Teleost fish eyes grow throughout life without compromising visual performance of the animal. This is made possible by a set of novel adaptations in the growth and development of the eye. Increased retinal area is achieved both by stretching the existing retina and by generation of new tissue at the retinal germinal zone at the margin of the eye. Rods are added in a fundamentally different fashion than are all other retinal cell types: they appear last as new retina is produced at the margin and they are inserted throughout the functional retina as it stretches. In this way, the animal maintains a constant rod density to preserve vision in low light level. Because the larger eye produces a larger image, visual acuity improves slightly as the animal grows. Adaptations responsible for regulation of retinal growth are analyzed and discussed.

    View details for Web of Science ID A1990FK90600020

    View details for PubMedID 1982493



    Disk membranes in the outer segment of rod photoreceptors are continuously renewed, being assembled at the outer segment base, displaced outward by new disks and eventually shed at the tip. In lower vertebrates, disk assembly occurs with a diurnal rhythm with 2-4% of the outer segment length produced daily. We have discovered that in toad and fish retinas the level of mRNA for opsin, the most abundant protein in rod disks, fluctuates with a daily rhythm and is regulated both by light and by a circadian oscillator. The mRNA level rises before light onset, remains high during the light phase of a diurnal cycle and decreases four to tenfold during the dark phase. In constant darkness, mRNA elevation occurs during subjective daytime. At night, rod opsin mRNA can be elevated by exposure to light.

    View details for Web of Science ID A1989T072000064

    View details for PubMedID 2521689



    A prominent dark facial stripe, the 'eyebar', is an important component of the reproductive coloration and dominance displays of 'barred' territorial male Haplochromis burtoni (Teleostei; Cichlidae). 'Barless' territorial males are identical to barred, behaviorally and morphologically, except they completely lack an eyebar during agonistic encounters with conspecifics. Both anatomical and physiological differences characterize eyebar pigment cells of barred and barless males. Melanophores and iridophores, which form a single structural and functional unit in the eyebar, contain less pigment in barless males. Physiologically, eyebar melanophores are tonically expanded in barred males, contracted in barless males. This physiological difference is correlated with a difference in the alpha adrenoceptor-mediated aggregation response of the cells in vitro: eyebar melanophores of barless males are significantly more responsive to physiological concentrations of the sympathetic neurotransmitter norepinephrine than those of barred males, and this intermorph difference appears to be unique to the eyebar color pattern. Physiological and morphological characteristics of eyebar pigment cells are functionally related. When barless males first begin to use the eyebar as a social display, the physiological state of melanophores changes from aggregation to dispersion. In subsequent weeks, additional pigment develops, which enhances conspicuousness of the display.

    View details for Web of Science ID A1987F775100011

    View details for PubMedID 3820135



    Territorial male Haplochromis burtoni (Teleostei; Cichlidae) have a dark facial stripe, the 'eyebar', which can appear and disappear within seconds, independently of other coloration patterns. It is used to signal territory ownership and aggressive intent. Some males, called 'barless', have functional melanophores in the eyebar region but never display this pattern, because melanin in eyebar pigment cells is never dispersed. The eyebar melanophores are controlled by a specialized branch of the maxillary nerve. Lesioning the 'eyebar nerve' resulted in immediate melanin dispersion and consequent darkening of the eyebar pattern, and it abolished the normal paling response in all behavioral situations. Nerve lesion produced similar results in both barred and barless males, except that the coloration of the denervated eyebar in barless males was more similar to camouflage markings than to the conspicuous black eyebar used as a social signal. Electrical stimulation of the maxillary nerve produced melanin aggregation. Photoelectric recordings of this paling response revealed no differences between barred and barless males, or between the eyebar and other facial chromatophores that do not function as visual displays. Thus, the difference in the physiological state of eyebar melanophores in intact barred and barless males cannot be explained by differences in peripheral nerve anatomy or physiology.

    View details for Web of Science ID A1987F775100010

    View details for PubMedID 3820134

  • Development of the optic tract in the cichlid fish Haplochromis burtoni. Brain research Presson, J. C., Fernald, R. D. 1986; 391 (2): 179-186


    In the teleost fish, Haplochromis burtoni, the optic tract is composed of 3 distinct components: the marginal tract, which projects to the optic tectum and is by far the largest, and the axial and medial tracts which project to diencephalic targets. In this paper we report on the normal development of these pathways in larval H. burtoni, an African cichlid fish. The earliest optic tract fibers are found in what will become the marginal optic tract. These fibers hug the wall of the diencephalon in a cohesive bundle. The first fibers in the axial tract location appear on day 5, increasing in number between days 6 and 18. Like marginal tract fibers, axial tract fibers form a cohesive bundle. It is not clear from these experiments whether the first axial tract fibers actually arrive at this location at day 5, or whether they are fibers arriving earlier that were physically displaced from the marginal tract at day 5. Medial tract fibers are not evident until day 6 of development and the number of medial tract fibers also increases as the animal gets older. Unlike fibers in the other two pathways, medial tract fibers do not travel together in a bundle. Rather, each one follows an independent trajectory to its target site. Comparison of this larval development with the adult optic tract organization which we have studied earlier suggests constraints on the mechanisms of axon guidance.

    View details for PubMedID 3697772



    Although teleost fish comprise the largest vertebrate radiation, surprisingly little is known about the structure and development of their central nervous systems. Since teleosts are being used much more frequently as model systems in neurobiological research, particularly in understanding visual function, detailed information is needed about central nervous system structures and interconnections. By using the Bodian method with Nissl counterstaining we have analyzed the major nuclei in the diencephalon and pretectum of a cichlid fish, Haplochromis burtoni, which is dependent on vision for its survival. Although our results are broadly comparable with those from other teleost species, there are clear differences, particularly among the visual nuclei. By using animals of a range of sizes to confirm our descriptions we were able to identify possible developmental relationships among several nuclei.

    View details for Web of Science ID A1985ANC7500006

    View details for PubMedID 4044911



    The organization of retinofugal projections was studied in a cichlid fish by labelling small groups of retinal ganglion cell axons with either horseradish peroxidase or cobaltous lysine. Two major findings resulted from these experiments. First, optic tract axons show a greater degree of pathway diversity than was previously appreciated, and this pathway diversity is related to the target nuclei of groups of axons. The most striking example is the formation of the medial optic tract. Fibers that will become the medial optic tract move abruptly away from their neighbors, at about the level of the optic chiasm, and coalesce at the dorsomedial edge of the marginal optic tract. The medial optic tract projects to the thalamus, the dorsal pretectum, and the deep layer of the optic tectum. The axial optic tract is a group of fibers which segregates from the most medial portion of the marginal optic tract, at about the level of the optic chiasm. The axial tract stays medial to the marginal optic tract for a few hundred microns and then curves laterally to rejoin the marginal optic tract. At least some axial trat axons terminate in the suprachiasmatic nucleus. Within the marginal optic tract, retinal ganglion cell axons from a given retinal quadrant are always segregated into at least two groups. The smaller group projects to the superficial pretectal nucleus. The larger group projects to the superficial layer of the optic tectum. Second, each nontectal retinal termination site receives a unique pattern of retinal input. Within the pretectum the parvocellular superficial pretectal nucleus receives a highly retinotopically organized input from all retinal regions; the basal optic nucleus receives a roughly retinotopically organized input from all retinal regions; the dorsal pretectum receives an input from all retinal regions; and the central pretectal nucleus receives input only from the ventral hemiretina. Within the diencephalon the thalamus receives an input from all retinal regions, but this input is not retinotopically organized; the suprachiasmatic nucleus receives input from the region of central retina that lies just dorsal to the optic nerve head, via the axial optic tract. The accessory optic nucleus receives input from the dorsal hemiretina.

    View details for Web of Science ID A1985AGX8100006

    View details for PubMedID 3998216



    Spectral sensitivity of the cichlid fish Haplochromis burtoni was measured under both scotopic and photopic conditions using a two-choice, food reward, operant conditioning paradigm. The highest absolute sensitivity (scotopic) is one quantum for every 5 to 50 rods measured at 475 nm (equivalent to a corneal irradiance of 3.8 x 10(6) Q s-1 cm-2). A P500(1) photopigment apparently mediates spectral sensitivity over most of the visible spectrum; microspectrophotometric studies of rods had previously shown them to contain this photopigment. However, the scotopic behavioral action spectrum shows a sensitivity to short wavelength light higher than is consistent with a P500(1) photopigment alone mediating the scotopic visual process. Determinations made under photopic conditions reveal a behavioral action spectrum broader than that found under scotopic conditions and consistent with mediation by interaction of the three known cone types in an opponent processing manner. The calculated photopic threshold value of approximately 10(4) Q s-1 (receptor)-1 is in agreement with results from other species and corresponds to a corneal irradiance of about 7 x 10(10) Q s-1 cm-2.

    View details for Web of Science ID A1985AQH8400008

    View details for PubMedID 3837089



    We have both measured directly and computed the amplitude of accommodation as a function of fish size to discover how the accommodative process changes during growth in the African cichlid fish, Haplochromis burtoni. We found that accommodation is achieved by lens movement in the pupillary plane along the naso-temporal axis. Accommodative lens movement is thereby directed toward a region of retinal specialization characterized by higher density of all cell types (except rods) in H. burtoni. When relaxed, the temporal retina is focused for near vision and active accommodation through lens movement adjusts the focus in the temporal retina for far vision. As the animal grows, the near and far focus points change appropriately for the fish size.

    View details for Web of Science ID A1985AFG4600003

    View details for PubMedID 4013084



    We have measured the chromatic aberration and optical resolution of the lens of the African cichlid fish, Haplochromis burtoni as a function of growth. We found that in H. burtoni, lenses of all sizes have a longitudinal chromatic aberration of ca 1.9% of the focal length. The resolution of the lens increases as the lens grows larger, presumably because diffraction effects decrease and any imperfections in the lens become relatively less significant. We found the lens in H. burtoni is very nearly diffraction limited so that a small lens (0.59 mm) has a resolution of 289 sec of arc and a large lens (2.90 mm) has a resolution of 66 sec of arc in red light (604 nm). This resolution is nearly ten times greater than can be resolved by the cone matrix.

    View details for Web of Science ID A1985AFG4600002

    View details for PubMedID 4013083



    Vertebrate lenses grow throughout life by the division of cells at the lens surface. The fibre cells thus produced are gradually covered by newer tissue, giving a layered structure. During growth, the lens must remain transparent and retain its refractile properties. The severity of these constraints is perhaps most evident in teleost fish which have a spherical lens that may increase in volume by a thousandfold during the first year of life. The dioptric power of the teleost fish eye is vested entirely in this spherical lens, as water, the cornea and the intraocular vitreous humour have almost identical refractive indices. Spherical lenses of uniform refractive index produce poor images because rays entering at different distances from the optic axis are focused at different distances from the lens. Teleost fish do not suffer from this imperfection and it has long been presumed that this is because there exists a refractive index gradient having a high value in the centre and decreasing continuously and symmetrically with radius in all directions. Here we demonstrate in the African cichlid fish, Haplochromis burtoni, that a refractive index gradient does exist, although its form is significantly different from that previously postulated.

    View details for Web of Science ID A1983QC04900053

    View details for PubMedID 6828142



    The retinal projections of the African cichlid fish, Haplochromis burtoni, have been traced by two different methods. Following unilateral enucleation, a modified Nauta technique was used to demonstrate degenerating axons and terminals. Some degeneration was found after 5 days but optimal survival time was 20-25 days. Orthograde transport of horseradish peroxidase (HRP) into the cut optic nerve also was used to examine retinal fiber distribution in the brain. The optic nerve is completely crossed and gives rise to two major tracts, the tractus opticus dorsomedialis and the tractus opticus ventrolateralis, as well as minor fascicles. Projections were found in the suprachiasmatic nucleus, ventral thalamus, dorsal thalamus, the pretectal complex, and the tectum opticum. The optic tectum is large and laminated and the great majority of the optic fibers terminate there. Degeneration methods revealed projections in the tectum to the stratum opticum, stratum griseum et fibrosum superficiale, and stratum album centrale. HRP staining confirmed these projections and revealed another projection to the stratum griseum centrale.

    View details for Web of Science ID A1982NQ28400005

    View details for PubMedID 7096633

  • GENESIS OF RODS IN TELEOST FISH RETINA NATURE JOHNS, P. R., Fernald, R. D. 1981; 293 (5828): 141-142

    View details for Web of Science ID A1981MF12500034

    View details for PubMedID 7266666


    View details for Web of Science ID A1981MR60100003

    View details for PubMedID 7336611


    View details for Web of Science ID A1980KR03500005

    View details for PubMedID 7467140


    View details for Web of Science ID A1980KS13800016

    View details for PubMedID 7210513



    The African cichlid fish Haplochromis burtoni shows specific behavioral responses to the intramuscular injection of testosterone. Approaching and attacking were significantly increased by injections, while six other observed behaviors remained unchanged. The results suggest that the injected testosterone affected the control of both sexual and agonistic behaviors.

    View details for Web of Science ID A1976CQ39600007

    View details for PubMedID 1002124


    View details for Web of Science ID A1975V982100020

    View details for PubMedID 1167830

  • A group of barbets. II. Quantitative measures. Zeitschrift für Tierpsychologie Fernald, R. D. 1973; 33 (3): 341-351

    View details for PubMedID 4785208


    View details for Web of Science ID A1972N893100007

    View details for PubMedID 4634317



    I have assembled a neuron model simulating contiguous patches of nerve cell membrane. With this model I have examined the functional significance of different spatial and temporal distributions of synaptic inputs. The model consists of two terminal electronic analogue circuits with inputs controlled by a LINC computer. One terminal represents the inside of a membrane patch, the other represents the outside. Two circuit designs are used: one simulates spike-generating regions of the neuron, the other simulates subthreshold activity in inexcitable regions. To simulate a neuron, patches are assembled in various spatial arrangements by suitable connection to the "intracellular" nodes. Thus the relation of neuron geometry to aspects of spatiotemporal summation of synaptic inputs can be investigated readily. Performance of the model is assessed by comparison with results from microelectrode studies in the cochlear nucleus of the cat. In particular, the peristimulus time (PST) histogram and averaged membrane potential are used for quantitative comparison. The model suggests that the geometry of the neuron's receptive surface can account for a wide variety of physiologically observed behavior, particularly in response to dynamic stimuli.

    View details for Web of Science ID A1971I995000001

    View details for PubMedID 4325425