The hypocretin (orexin) system: from a neural circuitry perspective.
2020; 167: 107993
Hypocretin/orexin neurons are distributed restrictively in the hypothalamus, a brain region known to orchestrate diverse functions including sleep, reward processing, food intake, thermogenesis, and mood. Since the hypocretins/orexins were discovered more than two decades ago, extensive studies have accumulated concrete evidence showing the pivotal role of hypocretin/orexin in diverse neural modulation. New method of viral-mediated tracing system offers the possibility to map the monosynaptic inputs and detailed anatomical connectivity of Hcrt neurons. With the development of powerful research techniques including optogenetics, fiber-photometry, cell-type/pathway specific manipulation and neuronal activity monitoring, as well as single-cell RNA sequencing, the details of how hypocretinergic system execute functional modulation of various behaviors are coming to light. In this review, we focus on the function of neural pathways from hypocretin neurons to target brain regions. Anatomical and functional inputs to hypocretin neurons are also discussed. We further briefly summarize the development of pharmaceutical compounds targeting hypocretin signaling. This article is part of the special issue on Neuropeptides.
View details for DOI 10.1016/j.neuropharm.2020.107993
View details for PubMedID 32135427
Hypothalamic circuitry underlying stress-induced insomnia and peripheral immunosuppression
2020; 6 (37)
View details for DOI 10.1126/sciadv.abc2590
Parallel circuits from the bed nuclei of stria terminalis to the lateral hypothalamus drive opposing emotional states.
Lateral hypothalamus (LH) neurons containing the neuropeptide hypocretin (HCRT; orexin) modulate affective components of arousal, but their relevant synaptic inputs remain poorly defined. Here we identified inputs onto LH neurons that originate from neuronal populations in the bed nuclei of stria terminalis (BNST; a heterogeneous region of extended amygdala). We characterized two non-overlapping LH-projecting GABAergic BNST subpopulations that express distinct neuropeptides (corticotropin-releasing factor, CRF, and cholecystokinin, CCK). To functionally interrogate BNSTLH circuitry, we used tools for monitoring and manipulating neural activity with cell-type-specific resolution in freely behaving mice. We found that Crf-BNST and Cck-BNST neurons respectively provide abundant and sparse inputs onto Hcrt-LH neurons, display discrete physiological responses to salient stimuli, drive opposite emotionally valenced behaviors, and receive different proportions of inputs from upstream networks. Together, our data provide an advanced model for how parallel BNSTLH pathways promote divergent emotional states via connectivity patterns of genetically defined, circuit-specific neuronal subpopulations.
View details for PubMedID 30038273
Optical Probing of Orexin/Hypocretin Receptor Antagonists.
The present study investigated the function of Hypocretin (Hcrt or Orexin/OX) receptor antagonists in sleep modulation and memory function with optical methods in transgenic mice.We used Hcrt-IRES-Cre knock-in mice and AAV vectors expressing channelrhodopsin-2 (ChR2) to render Hcrt neurons sensitive to blue light stimulation. We optogenetically stimulated Hcrt neurons and measured latencies to wakefulness in the presence or absence of OX1/2R antagonists and Zolpidem. We also examined endogenous Hcrt neuronal activity with fiber photometry. Changes in memory after optogenetic sleep disruption were evaluated by the novel object recognition test (NOR) and compared for groups treated with vehicle, OX1/2R antagonists, or Zolpidem. We also analyzed EEG power spectra of wakefulness, rapid eye movement (REM) sleep, and non-REM (NREM) sleep following the injections of vehicle, OX1/2R antagonists, and Zolpidem in young adult mice.Acute optogenetic stimulation of Hcrt neurons at different frequencies resulted in wakefulness. Treatment with dual OX1/2R antagonists (DORAs) DORA12 and MK6096, as well as selective OX2R antagonist MK1064 and Zolpidem, but not selective OX1R antagonist 1SORA1, significantly reduced the bout length of optogenetic stimulation-evoked wakefulness episode. Fiber photometry recordings of GCaMP6f signals showed that Hcrt neurons are active during wakefulness, even in the presence of OXR antagonists. Treatment with dual OX1/2R antagonists improved memory function despite optogenetic sleep fragmentation caused impaired memory function in a NOR test.Our results show DORAs and selective OX2R antagonists stabilize sleep and improve sleep-dependent cognitive processes even when challenged by optogenetic stimulation mimicking highly arousing stimuli.
View details for PubMedID 30060151
In vivo cell type-specific CRISPR knockdown of dopamine beta hydroxylase reduces locus coeruleus evoked wakefulness
View details for DOI 10.1038/s41467-018-07566-3
Brain Circuit of Claustrophobia-like Behavior in Mice Identified by Upstream Tracing of Sighing.
2020; 31 (11): 107779
Emotions are distinct patterns of behavioral and physiological responses triggered by stimuli that induce different brain states. Elucidating the circuits is difficult because of challenges in interrogating emotional brain states and their complex outputs. Here, we leverage the recent discovery in mice of a neural circuit for sighing, a simple, quantifiable output of various emotions. We show that mouse confinement triggers sighing, and this "claustrophobic" sighing, but not accompanying tachypnea, requires the same medullary neuromedin B (Nmb)-expressing neurons as physiological sighing. Retrograde tracing from the Nmb neurons identified 12 forebrain centers providing presynaptic input, including hypocretin (Hcrt)-expressing lateral hypothalamic neurons. Confinement activates Hcrt neurons, and optogenetic activation induces sighing and tachypnea whereas pharmacologic inhibition suppresses both responses. The effect on sighing is mediated by HCRT directly on Nmbneurons. We propose that this HCRT-NMB neuropeptide relay circuit mediates claustrophobic sighing and that activated Hcrt neurons are a claustrophobia brain state that directly controls claustrophobic outputs.
View details for DOI 10.1016/j.celrep.2020.107779
View details for PubMedID 32553161
Hypocretins and Arousal.
Current topics in behavioral neurosciences
How the brain controls vigilance state transitions remains to be fully understood. The discovery of hypocretins, also known as orexins, and their link to narcolepsy has undoubtedly allowed us to advance our knowledge on key mechanisms controlling the boundaries and transitions between sleep and wakefulness. Lack of function of hypocretin neurons (a relatively simple and non-redundant neuronal system) results in inappropriate control of sleep states without affecting the total amount of sleep or homeostatic mechanisms. Anatomical and functional evidence shows that the hypothalamic neurons that produce hypocretins/orexins project widely throughout the entire brain and interact with major neuromodulator systems in order to regulate physiological processes underlying wakefulness, attention, and emotions. Here, we review the role of hypocretins/orexins in arousal state transitions, and discuss possible mechanisms by which such a relatively small population of neurons controls fundamental brain state dynamics.
View details for DOI 10.1007/7854_2016_58
View details for PubMedID 28012091
In vivo assessment of behavioral recovery and circulatory exchange in the peritoneal parabiosis model
The sharing of circulation between two animals using a surgical procedure known as parabiosis has created a wealth of information towards our understanding of physiology, most recently in the neuroscience arena. The systemic milieu is a complex reservoir of tissues, immune cells, and circulating molecules that is surprisingly not well understood in terms of its communication across organ systems. While the model has been used to probe complex physiological questions for many years, critical parameters of recovery and exchange kinetics remain incompletely characterized, limiting the ability to design experiments and interpret results for complex questions. Here we provide evidence that mice joined by parabiosis gradually recover much physiology relevant to the study of brain function. Specifically, we describe the timecourse for a variety of recovery parameters, including those for general health and metabolism, motor coordination, activity, and sleep behavior. Finally, we describe the kinetics of chimerism for several lymphocyte populations as well as the uptake of small molecules into the brains of mice following parabiosis. Our characterization provides an important resource to those attempting to understand the complex interplay between the immune system and the brain as well as other organ systems.
View details for DOI 10.1038/srep29015
View details for Web of Science ID 000378851500002
View details for PubMedID 27364522
View details for PubMedCentralID PMC4929497
D4 Receptor Activation Differentially Modulates Hippocampal Basal and Apical Dendritic Synapses in Freely Moving Mice
2016; 26 (2): 647–55
Activation of D4 receptors (D4Rs) has been shown to improve cognitive performance, potentially affecting synaptic strength. We investigated the D4R agonist PD 168077 (PD) in hippocampal CA1 of freely moving mice. We electrically stimulated in stratum oriens (OR) or radiatum (RAD) and evoked local field potentials (LFPs). Intraperitoneally injected PD dose-dependently and reversibly attenuated LFPs for longer time in basal (OR) than apical (RAD) dendrites. High-frequency stimulation induced LTP that was stronger and more stable in OR than RAD. LTP lasted at least 4 h during which the paired-pulse ratio remained reduced. A PD concentration not affecting synaptic transmission was sufficient to reduce LTP in OR but not in RAD. A PD concentration reducing synaptic transmission reduced the early phase LTP in OR additionally and the late phase LTP in RAD exclusively. Furthermore, cell type-specific expression of mCherry in DATCre mice generated fluorescence in dorsal CA1 that was highest in lacunosum moleculare and similar in OR/RAD, indicating that midbrain dopaminergic fibers distribute evenly in OR/RAD. Together, the D4R-mediated modulation of hippocampal synaptic transmission and plasticity is stronger in OR than RAD. This could affect information processing in CA1 neurons, since signals arriving via basal and apical afferents are distinct.
View details for DOI 10.1093/cercor/bhu229
View details for Web of Science ID 000371522500018
View details for PubMedID 25270308
Hypocretins, Neural Systems, Physiology, and Psychiatric Disorders.
Current psychiatry reports
2016; 18 (1): 7-?
The hypocretins (Hcrts), also known as orexins, have been among the most intensely studied neuropeptide systems since their discovery about two decades ago. Anatomical evidence shows that the hypothalamic neurons that produce hypocretins/orexins project widely throughout the entire brain, innervating the noradrenergic locus coeruleus, the cholinergic basal forebrain, the dopaminergic ventral tegmental area, the serotonergic raphe nuclei, the histaminergic tuberomammillary nucleus, and many other brain regions. By interacting with other neural systems, the Hcrt system profoundly modulates versatile physiological processes including arousal, food intake, emotion, attention, and reward. Importantly, interruption of the interactions between these systems has the potential to cause neurological and psychiatric diseases. Here, we review the modulation of diverse neural systems by Hcrts and summarize potential therapeutic strategies based on our understanding of the Hcrt system's role in physiology and pathophysiological processes.
View details for DOI 10.1007/s11920-015-0639-0
View details for PubMedID 26733323
Controlled variations in stimulus similarity during learning determine visual discrimination capacity in freely moving mice
2013; 3: 1048
The mouse is receiving growing interest as a model organism for studying visual perception. However, little is known about how discrimination and learning interact to produce visual conditioned responses. Here, we adapted a two-alternative forced-choice visual discrimination task for mice and examined how training with equiprobable stimuli of varying similarity influenced conditioned response and discrimination performance as a function of learning. Our results indicate that the slope of the gradients in similarity during training determined the learning rate, the maximum performance and the threshold for successful discrimination. Moreover, the learning process obeyed an inverse relationship between discrimination performance and discriminative resolution, implying that sensitivity within a similarity range cannot be improved without sacrificing performance in another. Our study demonstrates how the interplay between discrimination and learning controls visual discrimination capacity and introduces a new training protocol with quantitative measures to study perceptual learning and visually-guided behavior in freely moving mice.
View details for DOI 10.1038/srep01048
View details for Web of Science ID 000313418100003
View details for PubMedID 23308341
View details for PubMedCentralID PMC3541512
Discrimination learning with variable stimulus 'salience'.
International archives of medicine
2011; 4 (1): 26-?
In nature, sensory stimuli are organized in heterogeneous combinations. Salient items from these combinations 'stand-out' from their surroundings and determine what and how we learn. Yet, the relationship between varying stimulus salience and discrimination learning remains unclear.A rigorous formulation of the problem of discrimination learning should account for varying salience effects. We hypothesize that structural variations in the environment where the conditioned stimulus (CS) is embedded will be a significant determinant of learning rate and retention level.Using numerical simulations, we show how a modified version of the Rescorla-Wagner model, an influential theory of associative learning, predicts relevant interactions between varying salience and discrimination learning.If supported by empirical data, our model will help to interpret critical experiments addressing the relations between attention, discrimination and learning.
View details for DOI 10.1186/1755-7682-4-26
View details for PubMedID 21812982
View details for PubMedCentralID PMC3176477
BEHAVIORAL ALTERATIONS ASSOCIATED WITH A DOWN REGULATION OF HCN1 mRNA IN HIPPOCAMPAL CORNUS AMMON 1 REGION AND NEOCORTEX AFTER CHRONIC INCOMPLETE GLOBAL CEREBRAL ISCHEMIA IN RATS
2010; 165 (3): 654–61
It has been suggested that hyperpolarization-activated cyclic-nucleotide-gated cation non-selective channel (HCN) 1 is primarily expressed in the hippocampus and can be regulated in many pathological settings. However, little is known about its change under ischemic conditions. In the present study, we performed neurophysiological recordings of sham-operated and chronic ischemic rats with hypoperfusion during the resolution of the neurological deficits respectively. In situ hybridization methods and reverse transcriptase-polymerase chain reaction (RT-PCR) assays were used to investigate whether and how HCN1 mRNA may be altered in global incomplete chronic cerebral ischemic rat model. Our results suggested that attenuated spatial learning and memory function of rats shown by longer escape latency, shorter time spent in the target quadrant and impaired long-term potentiation (LTP) after chronic cerebral ischemia. In the in situ hybridization cytochemistry experiment, HCN1 mRNA declined to 52.00% and 46.00% of the control values in the cornus ammon 1 (CA1) regions of hippocampus and neocortex separately after chronic cerebral ischemia. HCN1 mRNA in the hippocampal CA1 region and neocortex was markedly down regulated by ischemia, reaching 48.90% and 45.80% of the control values respectively in the semi-quantitative RT-PCR experiment. The phenomenon opened new insights for further investigation of the physiological and pathological significances of HCN1 in chronic incomplete global cerebral ischemia.
View details for DOI 10.1016/j.neuroscience.2009.10.053
View details for Web of Science ID 000274002600003
View details for PubMedID 19892002