Councilor, Society for Neuroscience (2006 - 2010)
Scientific Advisory Board, Seaside Therapeutics (2007 - 2009)
Scientific Advisory Board, Pfizer (2008 - 2009)
Honors & Awards
Medical Research Award in Neuropsychiatry, Robert and Claire Pasarow Foundation (2011)
Member, National Academy of Sciences (2011)
Fellow, American Academy of Arts and Sciences (2005)
Member, Institute of Medicine of the National Academies (2004)
Associate, Neurosciences Research Program (1999-2006)
Basic Neuroscience Research Award, Collegium Internationale Neuropsychopharmacologicum-Lilly (2002)
International Prize in Neuroscience, Dargut and Milena Kemali Foundation (2000)
Daniel Efron Award, American College of Neuropsychopharmacology (1998)
Distinguished Alumni Award, Stanford Medical School (1998)
Young Investigator Award, Society for Neuroscience (1993)
Current Research and Scholarly Interests
Long-lasting activity-dependent changes in the efficacy of synaptic transmission play an important role in the development of neural circuits and may mediate many forms of learning and memory. Work from my laboratory over the last 10 years has demonstrated that there are a variety of related but mechanistically distinct forms of synaptic plasticity. A major goal of my laboratory is to elucidate both the specific molecular events that are responsible for the triggering of these various forms of synaptic plasticity and the exact modifications in synaptic proteins that are responsible for the observed, long-lasting changes in synaptic efficacy. To accomplish this we use cellular electrophysiological recording techniques to examine synaptic plasticity in a variety of different in vitro preparations including thin slices of various regions of the rodent brain and primary neurons in culture. We also use cell biological and molecular techniques to examine the activity-dependent modulation of neurotransmitter receptors and to express dominant negative forms of various synaptic proteins so that their exact functions can be determined. An additional complementary approach has involved examining synaptic physiology and synaptic plasticity in various mutant mouse lines lacking specific synaptic proteins.
A related but independent area of research in my laboratory is the elucidation of the synaptic action of drugs of abuse such as the psychostimulants cocaine and amphetamine. Toward this end, we have developed in vitro slice preparations of the nucleus accumbens and ventral tegmental area, brain regions which are thought to mediate several of the behavioral effects of drugs of abuse. We have characterized a novel form of synaptic plasticity in the nucleus accumbens and have done an extensive pharmacological characterization of the synaptic effects of dopamine, cocaine, and amphetamine. Currently we are examining in more detail the underlying mechanisms of dopamine's actions and determining how chronic treatment with drugs of abuse affect the synaptic responses of nucleus accumbens and ventral tegmental area cells. Because chronic exposure to drugs of abuse elicit long-term adaptive changes in critical neural circuits, it is hoped that the knowledge gained from the work on the molecular mechanisms underlying synaptic plasticity will provide important clues to the molecular mechanisms underlying the development of tolerance, dependence and addiction.
Independent Studies (9)
- Directed Reading in Neurosciences
NEPR 299 (Aut, Win, Spr, Sum)
- Directed Reading in Psychiatry
PSYC 299 (Aut, Win, Spr, Sum)
- Graduate Research
NEPR 399 (Aut, Win, Spr, Sum)
- Graduate Research
PSYC 399 (Aut, Win, Spr, Sum)
- Medical Scholars Research
PSYC 370 (Aut, Win, Spr, Sum)
- Out-of-Department Advanced Research Laboratory in Experimental Biology
BIO 199X (Sum)
- Out-of-Department Graduate Research
BIO 300X (Aut, Win, Spr)
- Teaching in Psychiatry
PSYC 290 (Aut, Win, Spr, Sum)
- Undergraduate Research
PSYC 199 (Aut, Win, Spr, Sum)
- Directed Reading in Neurosciences
Graduate and Fellowship Programs
Leucine-Rich Repeat Transmembrane Proteins Are Essential for Maintenance of Long-Term Potentiation
2013; 79 (3): 439-446
Leucine-rich repeat transmembrane proteins (LRRTMs) are synaptic cell adhesion molecules that trigger excitatory synapse assembly in cultured neurons and influence synaptic function in vivo, but their role in synaptic plasticity is unknown. shRNA-mediated knockdown (KD) of LRRTM1 and LRRTM2 in vivo in CA1 pyramidal neurons of newborn mice blocked long-term potentiation (LTP) in acute hippocampal slices. Molecular replacement experiments revealed that the LRRTM2 extracellular domain is sufficient for LTP, probably because it mediates binding to neurexins (Nrxs). Examination of surface expression of endogenous AMPA receptors (AMPARs) in cultured neurons suggests that LRRTMs maintain newly delivered AMPARs at synapses after LTP induction. LRRTMs are also required for LTP of mature synapses on adult CA1 pyramidal neurons, indicating that the block of LTP in neonatal synapses by LRRTM1 and LRRTM2 KD is not due to impairment of synapse maturation.
View details for DOI 10.1016/j.neuron.2013.06.007
View details for Web of Science ID 000323085100006
Diverging neural pathways assemble a behavioural state from separable features in anxiety
2013; 496 (7444): 219-223
Behavioural states in mammals, such as the anxious state, are characterized by several features that are coordinately regulated by diverse nervous system outputs, ranging from behavioural choice patterns to changes in physiology (in anxiety, exemplified respectively by risk-avoidance and respiratory rate alterations). Here we investigate if and how defined neural projections arising from a single coordinating brain region in mice could mediate diverse features of anxiety. Integrating behavioural assays, in vivo and in vitro electrophysiology, respiratory physiology and optogenetics, we identify a surprising new role for the bed nucleus of the stria terminalis (BNST) in the coordinated modulation of diverse anxiety features. First, two BNST subregions were unexpectedly found to exert opposite effects on the anxious state: oval BNST activity promoted several independent anxious state features, whereas anterodorsal BNST-associated activity exerted anxiolytic influence for the same features. Notably, we found that three distinct anterodorsal BNST efferent projections-to the lateral hypothalamus, parabrachial nucleus and ventral tegmental area-each implemented an independent feature of anxiolysis: reduced risk-avoidance, reduced respiratory rate, and increased positive valence, respectively. Furthermore, selective inhibition of corresponding circuit elements in freely moving mice showed opposing behavioural effects compared with excitation, and in vivo recordings during free behaviour showed native spiking patterns in anterodorsal BNST neurons that differentiated safe and anxiogenic environments. These results demonstrate that distinct BNST subregions exert opposite effects in modulating anxiety, establish separable anxiolytic roles for different anterodorsal BNST projections, and illustrate circuit mechanisms underlying selection of features for the assembly of the anxious state.
View details for DOI 10.1038/nature12018
View details for Web of Science ID 000317346300041
LTP Requires a Unique Postsynaptic SNARE Fusion Machinery
2013; 77 (3): 542-558
Membrane fusion during exocytosis is mediated by assemblies of SNARE (soluble NSF-attachment protein receptor) and SM (Sec1/Munc18-like) proteins. The SNARE/SM proteins involved in vesicle fusion during neurotransmitter release are well understood, whereas little is known about the protein machinery that mediates activity-dependent AMPA receptor (AMPAR) exocytosis during long-term potentiation (LTP). Using direct measurements of LTP in acute hippocampal slices and an in vitro LTP model of stimulated AMPAR exocytosis, we demonstrate that the Q-SNARE proteins syntaxin-3 and SNAP-47 are required for regulated AMPAR exocytosis during LTP but not for constitutive basal AMPAR exocytosis. In contrast, the R-SNARE protein synaptobrevin-2/VAMP2 contributes to both regulated and constitutive AMPAR exocytosis. Both the central complexin-binding and the N-terminal Munc18-binding sites of syntaxin-3 are essential for its postsynaptic role in LTP. Thus, postsynaptic exocytosis of AMPARs during LTP is mediated by a unique fusion machinery that is distinct from that used during presynaptic neurotransmitter release.
View details for DOI 10.1016/j.neuron.2012.11.029
View details for Web of Science ID 000317030800015
View details for PubMedID 23395379
Input-specific control of reward and aversion in the ventral tegmental area
2012; 491 (7423): 212-?
Ventral tegmental area (VTA) dopamine neurons have important roles in adaptive and pathological brain functions related to reward and motivation. However, it is unknown whether subpopulations of VTA dopamine neurons participate in distinct circuits that encode different motivational signatures, and whether inputs to the VTA differentially modulate such circuits. Here we show that, because of differences in synaptic connectivity, activation of inputs to the VTA from the laterodorsal tegmentum and the lateral habenula elicit reward and aversion in mice, respectively. Laterodorsal tegmentum neurons preferentially synapse on dopamine neurons projecting to the nucleus accumbens lateral shell, whereas lateral habenula neurons synapse primarily on dopamine neurons projecting to the medial prefrontal cortex as well as on GABAergic (?-aminobutyric-acid-containing) neurons in the rostromedial tegmental nucleus. These results establish that distinct VTA circuits generate reward and aversion, and thereby provide a new framework for understanding the circuit basis of adaptive and pathological motivated behaviours.
View details for DOI 10.1038/nature11527
View details for Web of Science ID 000310774300035
View details for PubMedID 23064228
Anhedonia requires MC4R-mediated synaptic adaptations in nucleus accumbens
2012; 487 (7406): 183-U64
Chronic stress is a strong diathesis for depression in humans and is used to generate animal models of depression. It commonly leads to several major symptoms of depression, including dysregulated feeding behaviour, anhedonia and behavioural despair. Although hypotheses defining the neural pathophysiology of depression have been proposed, the critical synaptic adaptations in key brain circuits that mediate stress-induced depressive symptoms remain poorly understood. Here we show that chronic stress in mice decreases the strength of excitatory synapses on D1 dopamine receptor-expressing nucleus accumbens medium spiny neurons owing to activation of the melanocortin 4 receptor. Stress-elicited increases in behavioural measurements of anhedonia, but not increases in measurements of behavioural despair, are prevented by blocking these melanocortin 4 receptor-mediated synaptic changes in vivo. These results establish that stress-elicited anhedonia requires a neuropeptide-triggered, cell-type-specific synaptic adaptation in the nucleus accumbens and that distinct circuit adaptations mediate other major symptoms of stress-elicited depression.
View details for DOI 10.1038/nature11160
View details for Web of Science ID 000306278900029
View details for PubMedID 22785313
Integrating synaptic plasticity and striatal circuit function in addiction
CURRENT OPINION IN NEUROBIOLOGY
2012; 22 (3): 545-551
Exposure to addictive drugs causes changes in synaptic function within the striatal complex, which can either mimic or interfere with the induction of synaptic plasticity. These synaptic adaptations include changes in the nucleus accumbens (NAc), a ventral striatal subregion important for drug reward and reinforcement, as well as the dorsal striatum, which may promote habitual drug use. As the behavioral effects of drugs of abuse are long-lasting, identifying persistent changes in striatal circuits induced by in vivo drug experience is of considerable importance. Within the striatum, drugs of abuse have been shown to induce modifications in dendritic morphology, ionotropic glutamate receptors (iGluR) and the induction of synaptic plasticity. Understanding the detailed molecular mechanisms underlying these changes in striatal circuit function will provide insight into how drugs of abuse usurp normal learning mechanisms to produce pathological behavior.
View details for DOI 10.1016/j.conb.2011.09.009
View details for Web of Science ID 000306634700024
View details for PubMedID 22000687
Distinct Neuronal Coding Schemes in Memory Revealed by Selective Erasure of Fast Synchronous Synaptic Transmission
2012; 73 (5): 990-1001
Neurons encode information by firing spikes in isolation or bursts and propagate information by spike-triggered neurotransmitter release that initiates synaptic transmission. Isolated spikes trigger neurotransmitter release unreliably but with high temporal precision. In contrast, bursts of spikes trigger neurotransmission reliably (i.e., boost transmission fidelity), but the resulting synaptic responses are temporally imprecise. However, the relative physiological importance of different spike-firing modes remains unclear. Here, we show that knockdown of synaptotagmin-1, the major Ca(2+) sensor for neurotransmitter release, abrogated neurotransmission evoked by isolated spikes but only delayed, without abolishing, neurotransmission evoked by bursts of spikes. Nevertheless, knockdown of synaptotagmin-1 in the hippocampal CA1 region did not impede acquisition of recent contextual fear memories, although it did impair the precision of such memories. In contrast, knockdown of synaptotagmin-1 in the prefrontal cortex impaired all remote fear memories. These results indicate that different brain circuits and types of memory employ distinct spike-coding schemes to encode and transmit information.
View details for DOI 10.1016/j.neuron.2011.12.036
View details for Web of Science ID 000301558600013
View details for PubMedID 22405208
Postsynaptic Complexin Controls AMPA Receptor Exocytosis during LTP
2012; 73 (2): 260-267
Long-term potentiation (LTP) is a compelling synaptic correlate of learning and memory. LTP induction requires NMDA receptor (NMDAR) activation, which triggers SNARE-dependent exocytosis of AMPA receptors (AMPARs). However, the molecular mechanisms mediating AMPAR exocytosis induced by NMDAR activation remain largely unknown. Here, we show that complexin, a protein that regulates neurotransmitter release via binding to SNARE complexes, is essential for AMPAR exocytosis during LTP but not for the constitutive AMPAR exocytosis that maintains basal synaptic strength. The regulated postsynaptic AMPAR exocytosis during LTP requires binding of complexin to SNARE complexes. In hippocampal neurons, presynaptic complexin acts together with synaptotagmin-1 to mediate neurotransmitter release. However, postsynaptic synaptotagmin-1 is not required for complexin-dependent AMPAR exocytosis during LTP. These results suggest a complexin-dependent molecular mechanism for regulating AMPAR delivery to synapses, a mechanism that is surprisingly similar to presynaptic exocytosis but controlled by regulators other than synaptotagmin-1.
View details for DOI 10.1016/j.neuron.2011.11.020
View details for Web of Science ID 000299761600008
View details for PubMedID 22284181
Comprehensive qPCR profiling of gene expression in single neuronal cells
2012; 7 (1): 118-127
A major challenge in neuronal stem cell biology lies in characterization of lineage-specific reprogrammed human neuronal cells, a process that necessitates the use of an assay sensitive to the single-cell level. Single-cell gene profiling can provide definitive evidence regarding the conversion of one cell type into another at a high level of resolution. The protocol we describe uses Fluidigm Biomark dynamic arrays for high-throughput expression profiling from single neuronal cells, assaying up to 96 independent samples with up to 96 quantitative PCR (qPCR) probes (equivalent to 9,216 reactions) in a single experiment, which can be completed within 2-3 d. The protocol enables simple and cost-effective profiling of several hundred transcripts from a single cell, and it could have numerous utilities.
View details for DOI 10.1038/nprot.2011.430
View details for Web of Science ID 000299108900011
View details for PubMedID 22193304
The neurexin ligands, neuroligins and leucine-rich repeat transmembrane proteins, perform convergent and divergent synaptic functions in vivo
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2011; 108 (40): 16502-16509
Synaptic cell adhesion molecules, including the neurexin ligands, neuroligins (NLs) and leucine-rich repeat transmembrane proteins (LRRTMs), are thought to organize synapse assembly and specify synapse function. To test the synaptic role of these molecules in vivo, we performed lentivirally mediated knockdown of NL3, LRRTM1, and LRRTM2 in CA1 pyramidal cells of WT and NL1 KO mice at postnatal day (P)0 (when synapses are forming) and P21 (when synapses are largely mature). P0 knockdown of NL3 in WT or NL1 KO neurons did not affect excitatory synaptic transmission, whereas P0 knockdown of LRRTM1 and LRRTM2 selectively reduced AMPA receptor-mediated synaptic currents. P0 triple knockdown of NL3 and both LRRTMs in NL1 KO mice yielded greater reductions in AMPA and NMDA receptor-mediated currents, suggesting functional redundancy between NLs and LRRTMs during early synapse development. In contrast, P21 knockdown of LRRTMs did not alter excitatory transmission, whereas NL manipulations supported a role for NL1 in maintaining NMDA receptor-mediated transmission. These results show that neurexin ligands in vivo form a dynamic synaptic cell adhesion network, with compensation between NLs and LRRTMs during early synapse development and functional divergence upon synapse maturation.
View details for DOI 10.1073/pnas.1114028108
View details for Web of Science ID 000295536000012
View details for PubMedID 21953696
Projection-Specific Modulation of Dopamine Neuron Synapses by Aversive and Rewarding Stimuli
2011; 70 (5): 855-862
Midbrain dopamine (DA) neurons are not homogeneous but differ in their molecular properties and responses to external stimuli. We examined whether the modulation of excitatory synapses on DA neurons by rewarding or aversive stimuli depends on the brain area to which these DA neurons project. We identified DA neuron subpopulations in slices after injection of "Retrobeads" into single target areas of adult mice and found differences in basal synaptic properties. Administration of cocaine selectively modified excitatory synapses on DA cells projecting to nucleus accumbens (NAc) medial shell while an aversive stimulus selectively modified synapses on DA cells projecting to medial prefrontal cortex. In contrast, synapses on DA neurons projecting to NAc lateral shell were modified by both rewarding and aversive stimuli, which presumably reflects saliency. These results suggest that the mesocorticolimbic DA system may be comprised of three anatomically distinct circuits, each modified by distinct aspects of motivationally relevant stimuli.
View details for DOI 10.1016/j.neuron.2011.03.025
View details for Web of Science ID 000291843500007
View details for PubMedID 21658580
Postsynaptic TRPV1 triggers cell type-specific long-term depression in the nucleus accumbens
2010; 13 (12): 1519-U107
Synaptic modifications in the nucleus accumbens (NAc) are important for adaptive and pathological reward-dependent learning. Medium spiny neurons (MSNs), the major cell type in the NAc, participate in two parallel circuits that subserve distinct behavioral functions, yet little is known about differences in their electrophysiological and synaptic properties. Using bacterial artificial chromosome transgenic mice, we found that synaptic activation of group I metabotropic glutamate receptors in NAc MSNs in the indirect, but not direct, pathway led to the production of endocannabinoids, which activated presynaptic CB1 receptors to trigger endocannabinoid-mediated long-term depression (eCB-LTD) as well as postsynaptic transient receptor potential vanilloid 1 (TRPV1) channels to trigger a form of LTD resulting from endocytosis of AMPA receptors. These results reveal a previously unknown action of TRPV1 channels and indicate that the postsynaptic generation of endocannabinoids can modulate synaptic strength in a cell type-specific fashion by activating distinct pre- and postsynaptic targets.
View details for DOI 10.1038/nn.2685
View details for Web of Science ID 000284525800017
View details for PubMedID 21076424
A calcineurin/AKAP complex is required for NMDA receptor-dependent long-term depression
2010; 13 (9): 1053-1055
AKAP79/150 is a protein scaffold that is thought to position specific kinases (protein kinase A and C) and phosphatases (calcineurin) in appropriate synaptic domains so that their activities can regulate excitatory synaptic strength. Using a viral-mediated molecular replacement strategy in rat hippocampal slices, we found that AKAP is required for NMDA receptor-dependent long-term depression solely because of its interaction with calcineurin.
View details for DOI 10.1038/nn.2613
View details for Web of Science ID 000281332600008
View details for PubMedID 20694001
Understanding Synapses: Past, Present, and Future
2008; 60 (3): 469-476
Classical physiological work by Katz, Eccles, and others revealed the central importance of synapses in brain function, and characterized the mechanisms involved in synaptic transmission. Building on this work, major advances in the past two decades have elucidated how synapses work molecularly. In the present perspective, we provide a short description of our personal view of these advances, suggest a series of important future questions about synapses, and discuss ideas about how best to achieve further progress in the field.
View details for DOI 10.1016/j.neuron.2008.10.011
View details for Web of Science ID 000260983800018
View details for PubMedID 18995821
Endocannabinoid-mediated rescue of striatal LTD and motor deficits in Parkinson's disease models
2007; 445 (7128): 643-647
The striatum is a major forebrain nucleus that integrates cortical and thalamic afferents and forms the input nucleus of the basal ganglia. Striatal projection neurons target the substantia nigra pars reticulata (direct pathway) or the lateral globus pallidus (indirect pathway). Imbalances between neural activity in these two pathways have been proposed to underlie the profound motor deficits observed in Parkinson's disease and Huntington's disease. However, little is known about differences in cellular and synaptic properties in these circuits. Indeed, current hypotheses suggest that these cells express similar forms of synaptic plasticity. Here we show that excitatory synapses onto indirect-pathway medium spiny neurons (MSNs) exhibit higher release probability and larger N-methyl-d-aspartate receptor currents than direct-pathway synapses. Moreover, indirect-pathway MSNs selectively express endocannabinoid-mediated long-term depression (eCB-LTD), which requires dopamine D2 receptor activation. In models of Parkinson's disease, indirect-pathway eCB-LTD is absent but is rescued by a D2 receptor agonist or inhibitors of endocannabinoid degradation. Administration of these drugs together in vivo reduces parkinsonian motor deficits, suggesting that endocannabinoid-mediated depression of indirect-pathway synapses has a critical role in the control of movement. These findings have implications for understanding the normal functions of the basal ganglia, and also suggest approaches for the development of therapeutic drugs for the treatment of striatal-based brain disorders.
View details for DOI 10.1038/nature05506
View details for Web of Science ID 000244039400043
View details for PubMedID 17287809
Reward and aversion in a heterogeneous midbrain dopamine system
2014; 76: 351-359
The ventral tegmental area (VTA) is a heterogeneous brain structure that serves a central role in motivation and reward processing. Abnormalities in the function of VTA dopamine (DA) neurons and the targets they influence are implicated in several prominent neuropsychiatric disorders including addiction and depression. Recent studies suggest that the midbrain DA system is composed of anatomically and functionally heterogeneous DA subpopulations with different axonal projections. These findings may explain a number of previously confusing observations that suggested a role for DA in processing both rewarding as well as aversive events. Here we will focus on recent advances in understanding the neural circuits mediating reward and aversion in the VTA and how stress as well as drugs of abuse, in particular cocaine, alter circuit function within a heterogeneous midbrain DA system. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.
View details for DOI 10.1016/j.neuropharm.2013.03.019
View details for Web of Science ID 000330083600016
View details for PubMedID 23578393
Presynaptic Neurexin-3 Alternative Splicing trans-Synaptically Controls Postsynaptic AMPA Receptor Trafficking
2013; 154 (1): 75-88
Neurexins are essential presynaptic cell adhesion molecules that are linked to schizophrenia and autism and are subject to extensive alternative splicing. Here, we used a genetic approach to test the physiological significance of neurexin alternative splicing. We generated knockin mice in which alternatively spliced sequence #4 (SS4) of neuexin-3 is constitutively included but can be selectively excised by cre-recombination. SS4 of neurexin-3 was chosen because it is highly regulated and controls neurexin binding to neuroligins, LRRTMs, and other ligands. Unexpectedly, constitutive inclusion of SS4 in presynaptic neurexin-3 decreased postsynaptic AMPA, but not NMDA receptor levels, and enhanced postsynaptic AMPA receptor endocytosis. Moreover, constitutive inclusion of SS4 in presynaptic neurexin-3 abrogated postsynaptic AMPA receptor recruitment during NMDA receptor-dependent LTP. These phenotypes were fully rescued by constitutive excision of SS4 in neurexin-3. Thus, alternative splicing of presynaptic neurexin-3 controls postsynaptic AMPA receptor trafficking, revealing an unanticipated alternative splicing mechanism for trans-synaptic regulation of synaptic strength and long-term plasticity.
View details for DOI 10.1016/j.cell.2013.05.060
View details for Web of Science ID 000321327900011
View details for PubMedID 23827676
Autism-associated neuroligin-3 mutations commonly disrupt tonic endocannabinoid signaling.
2013; 78 (3): 498-509
Neuroligins are postsynaptic cell-adhesion molecules that interact with presynaptic neurexins. Rare mutations in neuroligins and neurexins predispose to autism, including a neuroligin-3 amino acid substitution (R451C) and a neuroligin-3 deletion. Previous analyses showed that neuroligin-3 R451C-knockin mice exhibit robust synaptic phenotypes but failed to uncover major changes in neuroligin-3 knockout mice, questioning the notion that a common synaptic mechanism mediates autism pathogenesis in patients with these mutations. Here, we used paired recordings in mice carrying these mutations to measure synaptic transmission at GABAergic synapses formed by hippocampal parvalbumin- and cholecystokinin-expressing basket cells onto pyramidal neurons. We demonstrate that in addition to unique gain-of-function effects produced by the neuroligin-3 R451C-knockin but not the neuroligin-3 knockout mutation, both mutations dramatically impaired tonic but not phasic endocannabinoid signaling. Our data thus suggest that neuroligin-3 is specifically required for tonic endocannabinoid signaling, raising the possibility that alterations in endocannabinoid signaling may contribute to autism pathophysiology.
View details for DOI 10.1016/j.neuron.2013.02.036
View details for PubMedID 23583622
Delta FosB differentially modulates nucleus accumbens direct and indirect pathway function
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2013; 110 (5): 1923-1928
Synaptic modifications in nucleus accumbens (NAc) medium spiny neurons (MSNs) play a key role in adaptive and pathological reward-dependent learning, including maladaptive responses involved in drug addiction. NAc MSNs participate in two parallel circuits, direct and indirect pathways that subserve distinct behavioral functions. Modification of NAc MSN synapses may occur in part via changes in the transcriptional potential of certain genes in a cell type–specific manner. The transcription factor ?FosB is one of the key proteins implicated in the gene expression changes in NAc caused by drugs of abuse, yet its effects on synaptic function in NAc MSNs are unknown. Here, we demonstrate that overexpression of ?FosB decreased excitatory synaptic strength and likely increased silent synapses onto D1 dopamine receptor–expressing direct pathway MSNs in both the NAc shell and core. In contrast, ?FosB likely decreased silent synapses onto NAc shell, but not core, D2 dopamine receptor–expressing indirect pathway MSNs. Analysis of NAc MSN dendritic spine morphology revealed that ?FosB increased the density of immature spines in D1 direct but not D2 indirect pathway MSNs. To determine the behavioral consequences of cell type-specific actions of ?FosB, we selectively overexpressed ?FosB in D1 direct or D2 indirect MSNs in NAc in vivo and found that direct (but not indirect) pathway MSN expression enhances behavioral responses to cocaine. These results reveal that ?FosB in NAc differentially modulates synaptic properties and reward-related behaviors in a cell type- and subregion-specific fashion.
View details for DOI 10.1073/pnas.1221742110
View details for Web of Science ID 000314558100069
View details for PubMedID 23319622
Candidate autism gene screen identifies critical role for cell-adhesion molecule CASPR2 in dendritic arborization and spine development
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2012; 109 (44): 18120-18125
Mutations in the contactin-associated protein 2 (CNTNAP2) gene encoding CASPR2, a neurexin-related cell-adhesion molecule, predispose to autism, but the function of CASPR2 in neural circuit assembly remains largely unknown. In a knockdown survey of autism candidate genes, we found that CASPR2 is required for normal development of neural networks. RNAi-mediated knockdown of CASPR2 produced a cell-autonomous decrease in dendritic arborization and spine development in pyramidal neurons, leading to a global decline in excitatory and inhibitory synapse numbers and a decrease in synaptic transmission without a detectable change in the properties of these synapses. Our data suggest that in addition to the previously described role of CASPR2 in mature neurons, where CASPR2 organizes nodal microdomains of myelinated axons, CASPR2 performs an earlier organizational function in developing neurons that is essential for neural circuit assembly and operates coincident with the time of autism spectrum disorder (ASD) pathogenesis.
View details for DOI 10.1073/pnas.1216398109
View details for Web of Science ID 000311149900087
View details for PubMedID 23074245
Dopaminergic Neurons from Midbrain-Specified Human Embryonic Stem Cell-Derived Neural Stem Cells Engrafted in a Monkey Model of Parkinson's Disease
2012; 7 (7)
The use of human embryonic stem cells (hESCs) to repair diseased or injured brain is promising technology with significant humanitarian, societal and economic impact. Parkinson's disease (PD) is a neurological disorder characterized by the loss of midbrain dopaminergic (DA) neurons. The generation of this cell type will fulfill a currently unmet therapeutic need. We report on the isolation and perpetuation of a midbrain-specified self-renewable human neural stem cell line (hNSCs) from hESCs. These hNSCs grew as a monolayer and uniformly expressed the neural precursor markers nestin, vimentin and a radial glial phenotype. We describe a process to direct the differentiation of these hNSCs towards the DA lineage. Glial conditioned media acted synergistically with fibroblastic growth factor and leukemia inhibitory factor to induce the expression of the DA marker, tyrosine hydroxylase (TH), in the hNSC progeny. The glial-derived neurotrophic factor did not fully mimic the effects of conditioned media. The hNSCs expressed the midbrain-specific transcription factors Nurr1 and Pitx3. The inductive effects did not modify the level of the glutamic acid decarboxylase (GAD) transcript, a marker for GABAergic neurons, while the TH transcript increased 10-fold. Immunocytochemical analysis demonstrated that the TH-expressing cells did not co-localize with GAD. The transplantation of these DA-induced hNSCs into the non-human primate MPTP model of PD demonstrated that the cells maintain their DA-induced phenotype, extend neurite outgrowths and express synaptic markers.
View details for Web of Science ID 000306507000069
View details for PubMedID 22815935
A Comparison of Striatal-Dependent Behaviors in Wild-Type and Hemizygous Drd1a and Drd2 BAC Transgenic Mice
JOURNAL OF NEUROSCIENCE
2012; 32 (27): 9119-9123
Studies of striatal physiology and motor control have increasingly relied on the use of bacterial artificial chromosome (BAC) transgenic mice expressing fluorophores or other genes under the control of genetic regulatory elements for the dopamine D1 receptor (D1R) or dopamine D2 receptor (D2R). Three recent studies have compared wild-type, D1R, and D2R BAC transgenic mice, and found significant differences in physiology and behavior, calling into question the use of these mice in studies of normal circuit function. We repeated the behavioral portions of these studies in wild-type C57BL/6 mice and hemizygous Drd1a-td Tomato (D1-Tmt), Drd1a-eGFP (D1-GFP), and Drd2-eGFP (D2-GFP) mice backcrossed into the C57BL/6 background. Our three laboratories independently found that open-field locomotion, acute locomotor responses to cocaine (20 mg/kg), locomotor sensitization to 5 d of daily injections of cocaine (15 mg/kg) or amphetamine (3 mg/kg), cocaine (20 mg/kg) conditioned place preference, and active avoidance learning to paired light and footshock were indistinguishable in these four mouse lines. These results suggest that while it is crucial to screen new transgenic mouse lines for abnormal behavior and physiology, these BAC transgenic mouse lines remain extremely valuable tools for evaluating the cellular, synaptic, and circuit basis of striatal motor control and associative learning.
View details for DOI 10.1523/JNEUROSCI.0224-12.2012
View details for Web of Science ID 000306193900002
View details for PubMedID 22764221
Autism-linked neuroligin-3 R451C mutation differentially alters hippocampal and cortical synaptic function
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2011; 108 (33): 13764-13769
Multiple independent mutations in neuroligin genes were identified in patients with familial autism, including the R451C substitution in neuroligin-3 (NL3). Previous studies showed that NL3(R451C) knock-in mice exhibited modestly impaired social behaviors, enhanced water maze learning abilities, and increased synaptic inhibition in the somatosensory cortex, and they suggested that the behavioral changes in these mice may be caused by a general shift of synaptic transmission to inhibition. Here, we confirm that NL3(R451C) mutant mice behaviorally exhibit social interaction deficits and electrophysiologically display increased synaptic inhibition in the somatosensory cortex. Unexpectedly, however, we find that the NL3(R451C) mutation produced a strikingly different phenotype in the hippocampus. Specifically, in the hippocampal CA1 region, the NL3(R451C) mutation caused an ?1.5-fold increase in AMPA receptor-mediated excitatory synaptic transmission, dramatically altered the kinetics of NMDA receptor-mediated synaptic responses, induced an approximately twofold up-regulation of NMDA receptors containing NR2B subunits, and enhanced long-term potentiation almost twofold. NL3 KO mice did not exhibit any of these changes. Quantitative light microscopy and EM revealed that the NL3(R451C) mutation increased dendritic branching and altered the structure of synapses in the stratum radiatum of the hippocampus. Thus, in NL3(R451C) mutant mice, a single point mutation in a synaptic cell adhesion molecule causes context-dependent changes in synaptic transmission; these changes are consistent with the broad impact of this mutation on murine and human behaviors, suggesting that NL3 controls excitatory and inhibitory synapse properties in a region- and circuit-specific manner.
View details for DOI 10.1073/pnas.1111093108
View details for Web of Science ID 000293895100079
View details for PubMedID 21808020
Neuroligins/LRRTMs prevent activity- and Ca2+/calmodulin-dependent synapse elimination in cultured neurons
JOURNAL OF CELL BIOLOGY
2011; 194 (2): 323-334
Neuroligins (NLs) and leucine-rich repeat transmembrane proteins (LRRTMs) are postsynaptic cell adhesion molecules that bind to presynaptic neurexins. In this paper, we show that short hairpin ribonucleic acid-mediated knockdowns (KDs) of LRRTM1, LRRTM2, and/or NL-3, alone or together as double or triple KDs (TKDs) in cultured hippocampal neurons, did not decrease synapse numbers. In neurons cultured from NL-1 knockout mice, however, TKD of LRRTMs and NL-3 induced an ?40% loss of excitatory but not inhibitory synapses. Strikingly, synapse loss triggered by the LRRTM/NL deficiency was abrogated by chronic blockade of synaptic activity as well as by chronic inhibition of Ca(2+) influx or Ca(2+)/calmodulin (CaM) kinases. Furthermore, postsynaptic KD of CaM prevented synapse loss in a cell-autonomous manner, an effect that was reversed by CaM rescue. Our results suggest that two neurexin ligands, LRRTMs and NLs, act redundantly to maintain excitatory synapses and that synapse elimination caused by the absence of NLs and LRRTMs is promoted by synaptic activity and mediated by a postsynaptic Ca(2+)/CaM-dependent signaling pathway.
View details for DOI 10.1083/jcb.201101072
View details for Web of Science ID 000293121700014
View details for PubMedID 21788371
Calcium Binding to PICK1 Is Essential for the Intracellular Retention of AMPA Receptors Underlying Long-Term Depression
JOURNAL OF NEUROSCIENCE
2010; 30 (49): 16437-16452
NMDA receptor (NMDAR)-dependent long-term depression (LTD) in the hippocampus is mediated primarily by the calcium-dependent removal of AMPA receptors (AMPARs) from the postsynaptic density. The AMPAR-binding, PDZ (PSD-95/Dlg/ZO1) and BAR (Bin/amphiphysin/Rvs) domain-containing protein PICK1 has been implicated in the regulation of AMPAR trafficking underlying several forms of synaptic plasticity. Using a strategy involving small hairpin RNA-mediated knockdown of PICK1 and its replacement with recombinant PICK1, we performed a detailed structure-function analysis of the role of PICK1 in hippocampal synaptic plasticity and the underlying NMDAR-induced AMPAR trafficking. We found that PICK1 is not necessary for maintenance of the basal synaptic complement of AMPARs or expression of either metabotropic glutamate receptor-dependent LTD or NMDAR-dependent LTP. Rather, PICK1 function is specific to NMDAR-dependent LTD and the underlying AMPAR trafficking. Furthermore, although PICK1 does not regulate the initial phase of NMDAR-induced AMPAR endocytosis, it is required for intracellular retention of internalized AMPARs. Detailed biophysical analysis of an N-terminal acidic motif indicated that it is involved in intramolecular electrostatic interactions that are disrupted by calcium. Mutations that interfered with the calcium-induced structural changes in PICK1 precluded LTD and the underlying NMDAR-induced intracellular retention of AMPARs. These findings support a model whereby calcium-induced modification of PICK1 structure is critical for its function in the retention of internalized AMPARs that underlies the expression of hippocampal NMDAR-dependent LTD.
View details for DOI 10.1523/JNEUROSCI.4478-10.2010
View details for Web of Science ID 000285089100005
View details for PubMedID 21147983
LRRTM2 Functions as a Neurexin Ligand in Promoting Excitatory Synapse Formation
2009; 64 (6): 791-798
Recently, leucine-rich repeat transmembrane proteins (LRRTMs) were found to be synaptic cell-adhesion molecules that, when expressed in nonneuronal cells, induce presynaptic differentiation in contacting axons. We now demonstrate that LRRTM2 induces only excitatory synapses, and that it also acts to induce synapses in transfected neurons similarly to neuroligin-1. Using affinity chromatography, we identified alpha- and beta-neurexins as LRRTM2 ligands, again rendering LRRTM2 similar to neuroligin-1. However, whereas neuroligins bind neurexins containing or lacking an insert in splice site #4, LRRTM2 only binds neurexins lacking an insert in splice site #4. Binding of neurexins to LRRTM2 can produce cell-adhesion junctions, consistent with a trans-interaction regulated by neurexin alternative splicing, and recombinant neurexin-1beta blocks LRRTM2's ability to promote presynaptic differentiation. Thus, our data suggest that two unrelated postsynaptic cell-adhesion molecules, LRRTMs and neuroligins, unexpectedly bind to neurexins as the same presynaptic receptor, but that their binding is subject to distinct regulatory mechanisms.
View details for DOI 10.1016/j.neuron.2009.12.012
View details for Web of Science ID 000273425800007
View details for PubMedID 20064387
N-methyl-d-aspartate receptor- and metabotropic glutamate receptor-dependent long-term depression are differentially regulated by the ubiquitin-proteasome system
EUROPEAN JOURNAL OF NEUROSCIENCE
2009; 30 (8): 1443-1450
Long-term depression (LTD) in CA1 pyramidal neurons can be induced by activation of either N-methyl-D-aspartate receptors (NMDARs) or metabotropic glutamate receptors (mGluRs), both of which elicit changes in synaptic efficacy through alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor (AMPAR) endocytosis. To address the role of the ubiquitin-proteasome system in regulating AMPAR endocytosis during these forms of LTD, we examined the effects of pharmacological inhibitors of proteasomal degradation and protein ubiquitination on endocytosis of glutamate receptor 1 (GluR1) -containing AMPARs in dissociated rat hippocampal cultures as well as LTD of excitatory synaptic responses in acute rat hippocampal slices. Our findings suggest that the contribution of the ubiquitin-proteasome system to NMDAR-induced vs. mGluR-induced AMPAR endocytosis and the consequent LTD differs significantly. NMDAR-induced AMPAR endocytosis and LTD occur independently of proteasome function but appear to depend, at least in part, on ubiquitination. In contrast, mGluR-induced AMPAR endocytosis and LTD are enhanced by inhibition of proteasomal degradation, as well as by the inhibitor of protein ubiquitination. Furthermore, the decay of mGluR-induced membrane depolarization and Erk activation is delayed following inhibition of either ubiquitination or proteasomal degradation. These results suggest that, although NMDAR-dependent LTD may utilize ubiquitin as a signal for AMPAR endocytosis, mGluR-induced signaling and LTD are limited by a feedback mechanism that involves the ubiquitin-proteasome system.
View details for DOI 10.1111/j.1460-9568.2009.06950.x
View details for Web of Science ID 000270958700001
View details for PubMedID 19821836
Molecular and Magnetic Resonance Imaging of Human Embryonic Stem Cell-Derived Neural Stem Cell Grafts in Ischemic Rat Brain
2009; 17 (7): 1282-1291
Real-time imaging of transplanted stem cells is essential for understanding their interactions in vivo with host environments, for tracking cell fate and function and for successful delivery and safety monitoring in the clinical setting. In this study, we used bioluminescence (BLI) and magnetic resonance imaging (MRI) to visualize the fate of grafted human embryonic stem cell (hESC)-derived human neural stem cells (hNSCs) in stroke-damaged rat brain. The hNSCs were genetically engineered with a lentiviral vector carrying a double fusion (DF) reporter gene that stably expressed enhanced green fluorescence protein (eGFP) and firefly luciferase (fLuc) reporter genes. The hNSCs were self-renewable, multipotent, and expressed markers for neural stem cells. Cell survival was tracked noninvasively by MRI and BLI for 2 months after transplantation and confirmed histologically. Electrophysiological recording from grafted GFP(+) cells and immuno-electronmicroscopy demonstrated connectivity. Grafted hNSCs differentiated into neurons, into oligodendrocytes in stroke regions undergoing remyelination and into astrocytes extending processes toward stroke-damaged vasculatures. Our data suggest that the combination of BLI and MRI modalities provides reliable real-time monitoring of cell fate.
View details for DOI 10.1038/mt.2009.104
View details for Web of Science ID 000267785800021
View details for PubMedID 19436269
A critical role for PSD-95/AKAP interactions in endocytosis of synaptic AMPA receptors
2009; 12 (2): 172-181
The endocytosis of AMPA receptors (AMPARs) underlies several forms of synaptic plasticity, including NMDA receptor (NMDAR)-dependent long-term depression (LTD), but the molecular mechanisms responsible for this trafficking remain unknown. We found that PSD-95, a major postsynaptic density protein, is important for NMDAR-triggered endocytosis of synaptic AMPARs in rat neuron cultures because of its binding to A kinase-anchoring protein 150 (AKAP150), a scaffold for specific protein kinases and phosphatases. Knockdown of PSD-95 with shRNA blocked NMDAR-triggered, but not constitutive or mGluR-triggered, endocytosis of AMPARs. Deletion of PSD-95's Src homology 3 and guanylate kinase-like domains, as well as a point mutation (L460P), both of which inhibit binding of PSD-95 to AKAP150, also blocked NMDAR-triggered AMPAR endocytosis. Furthermore, expression of a mutant AKAP150 that does not bind calcineurin inhibited this NMDAR-triggered trafficking event. Our results suggest that PSD-95's interaction with AKAP150 is critical for NMDAR-triggered AMPAR endocytosis and LTD, possibly because these scaffolds position calcineurin in the appropriate subsynaptic domain.
View details for DOI 10.1038/nn.2249
View details for Web of Science ID 000263182000018
View details for PubMedID 19169250
Functional Engraftment of the Medial Ganglionic Eminence Cells in Experimental Stroke Model
2009; 18 (7): 815-826
Currently there are no effective treatments targeting residual anatomical and behavioral deficits resulting from stroke. Evidence suggests that cell transplantation therapy may enhance functional recovery after stroke through multiple mechanisms. We used a syngeneic model of neural transplantation to explore graft-host communications that enhance cellular engraftment.The medial ganglionic eminence (MGE) cells were derived from 15-day-old transgenic rat embryos carrying green fluorescent protein (GFP), a marker, to easily track the transplanted cells. Adult rats were subjected to transient intraluminal occlusion of the medial cerebral artery. Two weeks after stroke, the grafts were deposited into four sites, along the rostro-caudal axis and medially to the stroke in the penumbra zone. Control groups included vehicle and fibroblast transplants. Animals were subjected to motor behavioral tests at 4 week posttransplant survival time. Morphological analysis demonstrated that the grafted MGE cells differentiated into multiple neuronal subtypes, established synaptic contact with host cells, increased the expression of synaptic markers, and enhanced axonal reorganization in the injured area. Initial patch-clamp recording demonstrated that the MGE cells received postsynaptic currents from host cells. Behavioral analysis showed reduced motor deficits in the rotarod and elevated body swing tests. These findings suggest that graft-host interactions influence the fate of grafted neural precursors and that functional recovery could be mediated by neurotrophic support, new synaptic circuit elaboration, and enhancement of the stroke-induced neuroplasticity.
View details for DOI 10.3727/096368909X470829
View details for Web of Science ID 000271253200013
View details for PubMedID 19500468
Mechanism and time course of cocaine-induced long-term potentiation in the ventral tegmental area
JOURNAL OF NEUROSCIENCE
2008; 28 (37): 9092-9100
Synaptic plasticity in the ventral tegmental area (VTA) has been implicated in the acquisition of a drug-dependent state. Even a single exposure to cocaine in naive animals is sufficient to trigger sustained changes on VTA glutamatergic synapses that resemble activity-dependent long-term potentiation (LTP) in other brain regions. However, an insight into its time course and mechanisms of action is limited. Here, we show that cocaine acts locally within the VTA to induce an LTP-like enhancement of AMPA receptor-mediated transmission that is not detectable minutes after drug exposure but is fully expressed within 3 h. This cocaine-induced LTP appears to be mediated via dopamine D(5) receptor activation of NMDA receptors and to require protein synthesis. Increased levels of high-conductance GluR1-containing AMPA receptors at synapses are evident at 3 h after cocaine exposure. Furthermore, our data suggest that cocaine-induced LTP might share the same molecular substrates for expression with activity-dependent LTP induced in the VTA by a spike-timing-dependent (STD) protocol, because we observed that STD LTP is significantly reduced or not inducible in VTA neurons previously exposed to cocaine in vivo or in vitro.
View details for DOI 10.1523/JNEUROSCI.1001-08.2008
View details for Web of Science ID 000259094800004
View details for PubMedID 18784289
Spike timing-dependent long-term potentiation in ventral tegmental area dopamine cells requires PKC
JOURNAL OF NEUROPHYSIOLOGY
2008; 100 (1): 533-538
Long-term potentiation (LTP) of excitatory synapses on ventral tegmental area (VTA) dopamine (DA) cells is thought to play an important role in mediating some of the behavioral effects of drugs of abuse yet little is known about its underlying mechanisms. We find that spike timing-dependent LTP (STD LTP) in VTA DA cells is absent in slices prepared from mice previously administered cocaine, suggesting that cocaine-induced LTP and STD LTP share underlying mechanisms. This form of STD LTP is dependent on NMDA receptor (NMDAR) activation and a rise in postsynaptic calcium but surprisingly was not affected by an inhibitor of calcium/calmodulin-dependent protein kinase II (CaMKII). It was blocked by antagonists of conventional isoforms of PKC, whereas activation of protein kinase C (PKC) using a phorbol ester enhanced synaptic strength. These results suggest that NMDAR-mediated activation of PKC, but not CaMKII, is a critical trigger for LTP in VTA DA cells.
View details for DOI 10.1152/jn.01384.2007
View details for Web of Science ID 000257635400048
View details for PubMedID 18450581
Molecular dissociation of the role of PSD-95 in regulating synaptic strength and LTD
2008; 57 (2): 248-262
The postsynaptic density protein PSD-95 influences synaptic AMPA receptor (AMPAR) content and may play a critical role in LTD. Here we demonstrate that the effects of PSD-95 on AMPAR-mediated synaptic responses and LTD can be dissociated. Our findings suggest that N-terminal-domain-mediated dimerization is important for PSD-95's effect on basal synaptic AMPAR function, whereas the C-terminal SH(3)-GK domains are also necessary for localizing PSD-95 to synapses. We identify PSD-95 point mutants (Q15A, E17R) that maintain PSD-95's influence on basal AMPAR synaptic responses yet block LTD. These point mutants increase the proteolysis of PSD-95 within its N-terminal domain, resulting in a C-terminal fragment that functions as a dominant negative likely by scavenging critical signaling proteins required for LTD. Thus, the C-terminal portion of PSD-95 serves a dual function. It is required to localize PSD-95 at synapses and as a scaffold for signaling proteins that are required for LTD.
View details for DOI 10.1016/j.neuron.2007.11.027
View details for Web of Science ID 000252758400009
View details for PubMedID 18215622
Endocytosis and recycling of AMPA receptors lacking GIuR2/3
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2008; 105 (3): 1038-1043
Excitatory synapses in the mammalian brain contain two types of ligand-gated ion channels: AMPA receptors (AMPARs) and NMDA receptors (NMDARs). AMPARs are responsible for generating excitatory synaptic responses, whereas NMDAR activation triggers long-lasting changes in these responses by modulating the trafficking of AMPARs toward and away from synapses. AMPARs are tetramers composed of four subunits (GluR1-GluR4), which current models suggest govern distinct AMPAR trafficking behavior during synaptic plasticity. Here, we address the roles of GluR2 and GluR3 in controlling the recycling- and activity-dependent endocytosis of AMPARs by using cultured hippocampal neurons prepared from knockout (KO) mice lacking these subunits. We find that synapses and dendritic spines form normally in cells lacking GluR2/3 and that upon NMDAR activation, GluR2/3-lacking AMPARs are endocytosed in a manner indistinguishable from GluR2-containing AMPARs in wild-type (WT) neurons. AMPARs lacking GluR2/3 also recycle to the plasma membrane identically to WT AMPARs. However, because of their permeability to calcium, GluR2-lacking but not WT AMPARs exhibited robust internalization throughout the dendritic tree in response to AMPA application. Dendritic endocytosis of AMPARs also was observed in GABAergic neurons, which express a high proportion of GluR2-lacking AMPARs. These results demonstrate that GluR2 and GluR3 are not required for activity-dependent endocytosis of AMPARs and suggest that the most important property of GluR2 in the context of AMPAR trafficking may be its influence on calcium permeability.
View details for DOI 10.1073/pnas.0711412105
View details for Web of Science ID 000252647900039
View details for PubMedID 18195348
Mechanisms underlying dedepression of synaptic NMDA receptors in the hippocampus
JOURNAL OF NEUROPHYSIOLOGY
2008; 99 (1): 254-263
N-Methyl-D-aspartate receptor (NMDAR)-mediated synaptic responses in hippocampal CA1 pyramidal cells are depressed during NMDAR-dependent long-term depression (LTD) due to mechanisms, in part, distinct from those underlying LTD of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated synaptic responses. The mechanisms underlying dedepression of synaptic NMDARs, however, are not known. We find that dedepression of NMDAR-mediated synaptic responses in the CA1 region of the rat hippocampus is input specific and does not require synaptic stimulation to be maintained. The induction of dedepression does not require activation of metabotropic glutamate receptors, L-type Ca(2+) channels, or release of Ca(2+) from intracellular stores. It does, however, rely on activation of NMDARs. In contrast to the dedepression of AMPAR-mediated synaptic responses, dedepression of NMDAR-mediated synaptic responses does not depend on activation of calcium/calmodulin-dependent protein kinase II, protein kinase C, cAMP-dependent protein kinase, or Src kinases. However, dedepression of synaptic NMDARs is significantly impaired by inhibitors of mitogen-activated protein kinase signaling. Specifically, inhibitors of extracellular signal-regulated kinase 1/2 prevented normal dedepression of synaptic NMDARs by a mechanism that did not require protein synthesis. These results provide further evidence that synaptic NMDARs can be bidirectionally modified by activity but by mechanisms distinct from those responsible for the activity-dependent, bidirectional modulation of synaptic AMPARs.
View details for DOI 10.1152/jn.01011.2007
View details for Web of Science ID 000252398500022
View details for PubMedID 17989241
Synaptic plasticity: Multiple forms, functions, and mechanisms
2008; 33 (1): 18-41
Experiences, whether they be learning in a classroom, a stressful event, or ingestion of a psychoactive substance, impact the brain by modifying the activity and organization of specific neural circuitry. A major mechanism by which the neural activity generated by an experience modifies brain function is via modifications of synaptic transmission; that is, synaptic plasticity. Here, we review current understanding of the mechanisms of the major forms of synaptic plasticity at excitatory synapses in the mammalian brain. We also provide examples of the possible developmental and behavioral functions of synaptic plasticity and how maladaptive synaptic plasticity may contribute to neuropsychiatric disorders.
View details for DOI 10.1038/sj.npp.1301559
View details for Web of Science ID 000251267100004
View details for PubMedID 17728696
Long-term monitoring of transplanted human neural stem cells in developmental and pathological contexts with MRI
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2007; 104 (24): 10211-10216
Noninvasive monitoring of stem cells, using high-resolution molecular imaging, will be instrumental to improve clinical neural transplantation strategies. We show that labeling of human central nervous system stem cells grown as neurospheres with magnetic nanoparticles does not adversely affect survival, migration, and differentiation or alter neuronal electrophysiological characteristics. Using MRI, we show that human central nervous system stem cells transplanted either to the neonatal, the adult, or the injured rodent brain respond to cues characteristic for the ambient microenvironment resulting in distinct migration patterns. Nanoparticle-labeled human central nervous system stem cells survive long-term and differentiate in a site-specific manner identical to that seen for transplants of unlabeled cells. We also demonstrate the impact of graft location on cell migration and describe magnetic resonance characteristics of graft cell death and subsequent clearance. Knowledge of migration patterns and implementation of noninvasive stem cell tracking might help to improve the design of future clinical neural stem cell transplantation.
View details for DOI 10.1073/pnas.0608519104
View details for Web of Science ID 000247363000053
View details for PubMedID 17553967
Mechanisms for synapse specificity during striatal long-term depression
JOURNAL OF NEUROSCIENCE
2007; 27 (19): 5260-5264
Endocannabinoid (eCB)-mediated forms of long-term synaptic plasticity occur in several brain regions, but much remains unknown about their basic properties and underlying mechanisms. Here, we present evidence that eCB-mediated long-term depression (eCB-LTD) at excitatory synapses on medium spiny neurons in the striatum requires presynaptic activity coincident with CB1 receptor activation. This dual requirement for CB1 activation and presynaptic activity is a mechanism by which eCB-LTD may be made synapse specific.
View details for DOI 10.1523/JNEUROSCI.0018-07.2007
View details for Web of Science ID 000246358500027
View details for PubMedID 17494712
Pharmacotherapy for cognitive impairment in a mouse model of Down syndrome
2007; 10 (4): 411-413
Ts65Dn mice, a model for Down syndrome, have excessive inhibition in the dentate gyrus, a condition that could compromise synaptic plasticity and mnemonic processing. We show that chronic systemic treatment of these mice with GABAA antagonists at non-epileptic doses causes a persistent post-drug recovery of cognition and long-term potentiation. These results suggest that over-inhibition contributes to intellectual disabilities associated with Down syndrome and that GABAA antagonists may be useful therapeutic agents for this disorder.
View details for DOI 10.1038/nn1860
View details for Web of Science ID 000245228600008
View details for PubMedID 17322876
Activation of NR2B-containing NMDA receptors is not required for NMDA receptor-dependent long-term depression
2007; 52 (1): 71-76
The triggering of both NMDA receptor-dependent long-term potentiation (LTP) and long-term depression (LTD) in the CA1 region of the hippocampus requires a rise in postsynaptic calcium. A prominent hypothesis has been that the detailed properties of this postsynaptic calcium signal dictate whether LTP or LTD is generated by a given pattern of synaptic activity. Recently, however, evidence has been presented that the subunit composition of the NMDA receptor (NMDAR) determines whether a synapse undergoes LTP or LTD with NR2A-containing NMDARs triggering LTP and NR2B-containing NMDARs triggering LTD. In the present study, the role of NR2B-containing synaptic NMDARs in the induction of LTD in CA1 pyramidal cells has been studied using the selective NR2B antagonists, ifenprodil and Ro25-6981. While both antagonists reduced NMDAR-mediated synaptic currents, neither prevented induction of LTD. These results demonstrate that activation of NR2B-containing NMDARs is not an absolute requirement for the induction of LTD in the hippocampus.
View details for DOI 10.1016/j.neuropharm.2006.07.005
View details for Web of Science ID 000243698200008
View details for PubMedID 16899258
Alternative N-terminal domains of PSD-95 and SAP97 govern activity-dependent regulation of synaptic AMPA receptor function
2006; 51 (1): 99-111
PSD-95 and SAP97 are scaffolding proteins that have been implicated in regulating AMPA receptor incorporation and function at synapses. Gain- and loss-of-function approaches, however, have generated conflicting results. To minimize adaptations during development and potential dominant-negative effects of overexpression, we have combined silencing of endogenous PSD-95 in mature neurons with heterologous expression of specific SAP97 or PSD-95 isoforms. We find that both PSD-95 and SAP97 contain alternative N termini expressing either double cysteines that normally are palmitoylated (alpha-isoforms) or an L27 domain (beta-isoforms). Whereas alpha-isoforms of PSD-95 and SAP97 influence AMPA receptor-mediated synaptic strength independent of activity, the effects of beta-isoforms are regulated by activity in a CaMKII-dependent manner. Importantly, the synaptic effects of the beta-isoforms are masked by the endogenous alpha-isoform of PSD-95. These results demonstrate that the different N termini of the predominant endogenous forms of PSD-95 (alpha-isoform) and SAP97 (beta-isoform) govern their role in regulating synaptic function.
View details for DOI 10.1016/j.neuron.2006.05.016
View details for Web of Science ID 000239037700013
View details for PubMedID 16815335
Substrate localization creates specificity in calcium/calmodulin-dependent protein kinase II signaling at synapses
JOURNAL OF BIOLOGICAL CHEMISTRY
2006; 281 (19): 13794-13804
Calcium/calmodulin-dependent protein kinase II (CaMKII), a major component of the postsynaptic density (PSD) of excitatory synapses, plays a key role in the regulation of synaptic function in the mammalian brain. Although many postsynaptic substrates for CaMKII have been characterized in vitro, relatively little is known about their phosphorylation in vivo. By tagging synaptic proteins with a peptide substrate specific for CaMKII and expressing them in cultured neurons, we have visualized substrate phosphorylation by CaMKII at intact synapses. All substrates tested were strongly phosphorylated by CaMKII in HEK293 cells. However, activity-dependent phosphorylation of substrates at synapses was highly selective in that the glutamate receptor subunits NR2B and GluR1 were poorly phosphorylated whereas PSD-95 and Stargazin, proteins implicated in the scaffolding and trafficking of AMPA receptors, were robustly phosphorylated. Phosphatase activity limited phosphorylation of Stargazin but not NR2B and GluR1. These results suggest that the unique molecular architecture of the PSD results in highly selective substrate discrimination by CaMKII.
View details for DOI 10.1074/jbc.M600966200
View details for Web of Science ID 000237336600090
View details for PubMedID 16551613
Synaptic scaling mediated by glial TNF-alpha
2006; 440 (7087): 1054-1059
Two general forms of synaptic plasticity that operate on different timescales are thought to contribute to the activity-dependent refinement of neural circuitry during development: (1) long-term potentiation (LTP) and long-term depression (LTD), which involve rapid adjustments in the strengths of individual synapses in response to specific patterns of correlated synaptic activity, and (2) homeostatic synaptic scaling, which entails uniform adjustments in the strength of all synapses on a cell in response to prolonged changes in the cell's electrical activity. Without homeostatic synaptic scaling, neural networks can become unstable and perform suboptimally. Although much is known about the mechanisms underlying LTP and LTD, little is known about the mechanisms responsible for synaptic scaling except that such scaling is due, at least in part, to alterations in receptor content at synapses. Here we show that synaptic scaling in response to prolonged blockade of activity is mediated by the pro-inflammatory cytokine tumour-necrosis factor-alpha (TNF-alpha). Using mixtures of wild-type and TNF-alpha-deficient neurons and glia, we also show that glia are the source of the TNF-alpha that is required for this form of synaptic scaling. We suggest that by modulating TNF-alpha levels, glia actively participate in the homeostatic activity-dependent regulation of synaptic connectivity.
View details for DOI 10.1038/nature04671
View details for Web of Science ID 000236906000037
View details for PubMedID 16547515
CREB modulates excitability of nucleus accumbens neurons
2006; 9 (4): 475-477
Drugs of abuse cause activation of the cyclic AMP response element binding protein (CREB) in the nucleus accumbens (NAc). Expression of active CREB in rat NAc medium spiny neurons (MSNs) increased their excitability, whereas dominant-negative CREB had the opposite effect. Decreasing excitability of NAc MSNs in vivo by overexpression of potassium channels enhanced locomotor responses to cocaine, suggesting that the increased NAc MSN excitability caused by CREB helped to limit behavioral sensitivity to cocaine.
View details for DOI 10.1038/nn1661
View details for Web of Science ID 000236310700010
View details for PubMedID 16520736
Transsynaptic signaling by postsynaptic synapse-associated protein 97
JOURNAL OF NEUROSCIENCE
2006; 26 (8): 2343-2357
The molecular mechanisms by which postsynaptic modifications lead to precisely coordinated changes in presynaptic structure and function are primarily unknown. To address this issue, we examined the presynaptic consequences of postsynaptic expression of members of the membrane-associated guanylate kinase family of synaptic scaffolding proteins. Postsynaptic expression of synapse-associated protein 97 (SAP97) increased presynaptic protein content and active zone size to a greater extent than comparable amounts of postsynaptic PSD-95 (postsynaptic density-95) or SAP102. In addition, postsynaptic expression of SAP97 enhanced presynaptic function, as measured by increased FM4-64 dye uptake. The structural presynaptic effects of postsynaptic SAP97 required ligand binding through two of its PDZ (PSD-95/Discs large/zona occludens-1) domains as well as intact N-terminal and guanylate kinase domains. Expression of SAP97 recruited a complex of additional postsynaptic proteins to synapses including glutamate receptor 1, Shank1a, SPAR (spine-associated RapGAP), and proSAP2. Furthermore, inhibition of several different transsynaptic signaling proteins including cadherins, integrins, and EphB receptor/ephrinB significantly reduced the presynaptic growth caused by postsynaptic SAP97. These results suggest that SAP97 may play a central role in the coordinated growth of synapses during development and plasticity by recruiting a complex of postsynaptic proteins that enhances presynaptic terminal growth and function via multiple transsynaptic molecular interactions.
View details for DOI 10.1523/JNEUROSCI.5247-05.2006
View details for Web of Science ID 000235515800024
View details for PubMedID 16495462
Neural mechanisms of addiction: The role of reward-related learning and memory
ANNUAL REVIEW OF NEUROSCIENCE
2006; 29: 565-598
Addiction is a state of compulsive drug use; despite treatment and other attempts to control drug taking, addiction tends to persist. Clinical and laboratory observations have converged on the hypothesis that addiction represents the pathological usurpation of neural processes that normally serve reward-related learning. The major substrates of persistent compulsive drug use are hypothesized to be molecular and cellular mechanisms that underlie long-term associative memories in several forebrain circuits (involving the ventral and dorsal striatum and prefrontal cortex) that receive input from midbrain dopamine neurons. Here we review progress in identifying candidate mechanisms of addiction.
View details for DOI 10.1146/annurev.neuro.29.051605.113009
View details for Web of Science ID 000239807800020
View details for PubMedID 16776597
A schizophrenia-related sensorimotor deficit links alpha 3-containing GABA(A) receptors to a dopamine hyperfunction
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2005; 102 (47): 17154-17159
Overactivity of the dopaminergic system in the brain is considered to be a contributing factor to the development and symptomatology of schizophrenia. Therefore, the GABAergic control of dopamine functions was assessed by disrupting the gene encoding the alpha3 subunit of the GABA(A) receptor. alpha3 knockout (alpha3KO) mice exhibited neither an obvious developmental defect nor apparent morphological brain abnormalities, and there was no evidence for compensatory up-regulation of other major GABA(A)-receptor subunits. Anxiety-related behavior in the elevated-plus-maze test was undisturbed, and the anxiolytic-like effect of diazepam, which is mediated by alpha2-containing GABA(A) receptors, was preserved. As a result of the loss of alpha3 GABA(A) receptors, the GABA-induced whole-cell current recorded from midbrain dopamine neurons was significantly reduced. Spontaneous locomotor activity was slightly elevated in alpha3KO mice. Most notably, prepulse inhibition of the acoustic startle reflex was markedly attenuated in the alpha3KO mice, pointing to a deficit in sensorimotor information processing. This deficit was completely normalized by treatment with the antipsychotic D2-receptor antagonist haloperidol. The amphetamine-induced hyperlocomotion was not altered in alpha3KO mice compared with WT mice. These results suggest that the absence of alpha3-subunit-containing GABA(A) receptors induces a hyperdopaminergic phenotype, including a severe deficit in sensorimotor gating, a common feature among psychiatric conditions, including schizophrenia. Hence, agonists acting at alpha3-containing GABA(A) receptors may constitute an avenue for an effective treatment of sensorimotor-gating deficits in various psychiatric conditions.
View details for DOI 10.1073/pnas.0508752102
View details for Web of Science ID 000233463200045
View details for PubMedID 16284244
Dopamine modulation of state-dependent endocannabinoid release and long-term depression in the striatum
JOURNAL OF NEUROSCIENCE
2005; 25 (45): 10537-10545
Endocannabinoids are important mediators of short- and long-term synaptic plasticity, but the mechanisms of endocannabinoid release have not been studied extensively outside the hippocampus and cerebellum. Here, we examined the mechanisms of endocannabinoid-mediated long-term depression (eCB-LTD) in the dorsal striatum, a brain region critical for motor control and reinforcement learning. Unlike other cell types, strong depolarization of medium spiny neurons was not sufficient to yield detectable endocannabinoid release. However, when paired with postsynaptic depolarization sufficient to activate L-type calcium channels, activation of postsynaptic metabotropic glutamate receptors (mGluRs), either by high-frequency tetanic stimulation or an agonist, induced eCB-LTD. Pairing bursts of afferent stimulation with brief subthreshold membrane depolarizations that mimicked down-state to up-state transitions also induced eCB-LTD, which not only required activation of mGluRs and L-type calcium channels but also was bidirectionally modulated by dopamine D2 receptors. Consistent with network models, these results demonstrate that dopamine regulates the induction of a Hebbian form of long-term synaptic plasticity in the striatum. However, this gating of plasticity by dopamine is accomplished via an unexpected mechanism involving the regulation of mGluR-dependent endocannabinoid release.
View details for DOI 10.1523/JNEUROSCI.2959-05.2005
View details for Web of Science ID 000233137000025
View details for PubMedID 16280591
GABA excitation in the adult brain: A mechanism for excitation-neurogenesis coupling
2005; 47 (6): 775-777
The production of new neurons in the adult hippocampus is exquisitely regulated, and alterations in this process may underlie both normal and pathological hippocampal function. In this issue of Neuron, Tozuka et al. describe electrophysiological recordings that target proliferating progenitor cells in adult mouse hippocampal slices. They report that GABAergic synaptic inputs directly depolarize the proliferating progenitors, thereby activating molecular players that favor neuronal differentiation and providing a mechanism for direct excitation-neurogenesis coupling in vivo.
View details for DOI 10.1016/j.neuron.2005.08.029
View details for Web of Science ID 000232085000003
View details for PubMedID 16157270
Distinct triggering and expression mechanisms underlie LTD of AMPA and NMDA synaptic responses
2005; 8 (8): 1043-1050
Although long-term depression (LTD) of AMPA receptor-mediated postsynaptic currents (AMPAR EPSCs) has been extensively examined, little is known about the mechanisms responsible for LTD of NMDA receptor (NMDAR)-mediated EPSCs. Here we show differences in the intracellular signaling cascades that mediate LTD of AMPAR EPSCs versus NMDAR EPSCs in rat hippocampus. Both forms of LTD were blocked by inhibitors of protein phosphatase 1, but only LTD of AMPAR EPSCs was affected by inhibition of calcineurin. Notably, in contrast to LTD of AMPAR EPSCs, LTD of NMDAR EPSCs was unaffected by endocytosis inhibitors. A role for calcium-dependent actin depolymerization in LTD of NMDAR EPSCs was supported by the findings that the actin stabilizer phalloidin and a cofilin inhibitory peptide each blocked LTD of NMDAR EPSCs but not AMPAR EPSCs. These results suggest that the same pattern of afferent activity elicits depression of AMPAR- and NMDAR-mediated synaptic responses by means of distinct triggering and expression mechanisms.
View details for DOI 10.1038/nn1506
View details for Web of Science ID 000230760200016
View details for PubMedID 16025109
Generation of silent synapses by acute in vivo expression of CaMKIV and CREB
2005; 45 (5): 741-752
The transcription factor CREB is critical for several forms of experience-dependent plasticity in a range of species and is commonly activated in neurons by calcium/calmodulin-dependent protein kinase IV (CaMKIV). Surprisingly, little is known about the neural circuit adaptations caused by activation of CaMKIV and CREB. Here, we use viral-mediated gene transfer in vivo to examine the consequences of acute expression of constitutively active forms of CaMKIV and CREB on synaptic function in the rodent hippocampus. Acute expression of active CaMKIV or CREB caused an enhancement of both NMDA receptor-mediated synaptic responses and long-term potentiation (LTP). This was accompanied by electrophysiological and morphological changes consistent with the generation of "silent synapses," which provide an ideal substrate for further experience-dependent modifications of neural circuitry and which may also be important for the consolidation of long-term synaptic plasticity and memories.
View details for DOI 10.1016/j.neuron.2005.01.039
View details for Web of Science ID 000227446700013
View details for PubMedID 15748849
LTP and LTD: An embarrassment of riches
2004; 44 (1): 5-21
LTP and LTD, the long-term potentiation and depression of excitatory synaptic transmission, are widespread phenomena expressed at possibly every excitatory synapse in the mammalian brain. It is now clear that "LTP" and "LTD" are not unitary phenomena. Their mechanisms vary depending on the synapses and circuits in which they operate. Here we review those forms of LTP and LTD for which mechanisms have been most firmly established. Examples are provided that show how these mechanisms can contribute to experience-dependent modifications of brain function.
View details for Web of Science ID 000224232600003
View details for PubMedID 15450156
Multiple roles for the active zone protein RIM1 alpha in late stages of neurotransmitter release
2004; 42 (6): 889-896
The active zone protein RIM1alpha interacts with multiple active zone and synaptic vesicle proteins and is implicated in short- and long-term synaptic plasticity, but it is unclear how RIM1alpha's biochemical interactions translate into physiological functions. To address this question, we analyzed synaptic transmission in autaptic neurons cultured from RIM1alpha-/- mice. Deletion of RIM1alpha causes a large reduction in the readily releasable pool of vesicles, alters short-term plasticity, and changes the properties of evoked asynchronous release. Lack of RIM1alpha, however, had no effect on synapse formation, spontaneous release, overall Ca2+ sensitivity of release, or synaptic vesicle recycling. These results suggest that RIM1alpha modulates sequential steps in synaptic vesicle exocytosis through serial protein-protein interactions and that this modulation is the basis for RIM1alpha's role in synaptic plasticity.
View details for Web of Science ID 000222329300005
View details for PubMedID 15207234
Excitation-neurogenesis coupling in adult neural stem/progenitor cells
2004; 42 (4): 535-552
A wide variety of in vivo manipulations influence neurogenesis in the adult hippocampus. It is not known, however, if adult neural stem/progenitor cells (NPCs) can intrinsically sense excitatory neural activity and thereby implement a direct coupling between excitation and neurogenesis. Moreover, the theoretical significance of activity-dependent neurogenesis in hippocampal-type memory processing networks has not been explored. Here we demonstrate that excitatory stimuli act directly on adult hippocampal NPCs to favor neuron production. The excitation is sensed via Ca(v)1.2/1.3 (L-type) Ca(2+) channels and NMDA receptors on the proliferating precursors. Excitation through this pathway acts to inhibit expression of the glial fate genes Hes1 and Id2 and increase expression of NeuroD, a positive regulator of neuronal differentiation. These activity-sensing properties of the adult NPCs, when applied as an "excitation-neurogenesis coupling rule" within a Hebbian neural network, predict significant advantages for both the temporary storage and the clearance of memories.
View details for Web of Science ID 000221708300006
View details for PubMedID 15157417
Activity-dependent regulation of dendritic synthesis and trafficking of AMPA receptors
2004; 7 (3): 244-253
Regulation of AMPA receptor (AMPAR) trafficking is important for neural plasticity. Here we examined the trafficking and synthesis of the GluR1 and GluR2 subunits using ReAsH-EDT(2) and FlAsH-EDT(2) staining. Activity blockade of rat cultured neurons increased dendritic GluR1, but not GluR2, levels. Examination of transected dendrites revealed that both AMPAR subunits were synthesized in dendrites and that activity blockade enhanced dendritic synthesis of GluR1 but not GluR2. In contrast, acute pharmacological manipulations increased dendritic synthesis of both subunits. AMPARs synthesized in dendrites were inserted into synaptic plasma membranes and, after activity blockade, the electrophysiological properties of native synaptic AMPARs changed in the manner predicted by the imaging experiments. In addition to providing a novel mechanism for synaptic modifications, these results point out the advantages of using FlAsH-EDT(2) and ReAsH-EDT(2) for studying the trafficking of newly synthesized proteins in local cellular compartments such as dendrites.
View details for DOI 10.1038/nn1189
View details for Web of Science ID 000189197900014
View details for PubMedID 14770185
beta-catenin is critical for dendritic morphogenesis
2003; 6 (11): 1169-1177
Regulated growth and arborization of dendritic processes are critical to the formation of functional neuronal networks. Here we identify beta-catenin as a critical mediator of dendritic morphogenesis. We found that increasing the intracellular levels of beta-catenin and other members of the cadherin/catenin complex, namely N-cadherin and alphaN-catenin, enhances dendritic arborization in rat hippocampal neurons, an effect that does not require Wnt/beta-catenin-dependent transcription. Conversely, proteins that sequester beta-catenin decreased dendritic branch tip number and total dendritic branch length. Enhancement of dendritic growth elicited by depolarization requires beta-catenin and increased Wnt release. These results identify Wnt/beta-catenin signaling as an important mediator of dendritic development and suggest that the intracellular level of the cadherin/catenin complex is a limiting factor during critical stages of dendritic morphogenesis.
View details for DOI 10.1038/nn1132
View details for Web of Science ID 000186229200016
View details for PubMedID 14528308
- Opinion - The long-term potential of LTP NATURE REVIEWS NEUROSCIENCE 2003; 4 (11): 923-926
Drugs of abuse and stress trigger a common synaptic adaptation in dopamine neurons
2003; 37 (4): 577-582
Drug seeking and drug self-administration in both animals and humans can be triggered by drugs of abuse themselves or by stressful events. Here, we demonstrate that in vivo administration of drugs of abuse with different molecular mechanisms of action as well as acute stress both increase strength at excitatory synapses on midbrain dopamine neurons. Psychoactive drugs with minimal abuse potential do not cause this change. The synaptic effects of stress, but not of cocaine, are blocked by the glucocorticoid receptor antagonist RU486. These results suggest that plasticity at excitatory synapses on dopamine neurons may be a key neural adaptation contributing to addiction and its interactions with stress and thus may be an attractive therapeutic target for reducing the risk of addiction.
View details for Web of Science ID 000181136500007
View details for PubMedID 12597856
A developmental switch in the signaling cascades for LTP induction
2003; 6 (1): 15-16
Long-term potentiation (LTP) is thought to be critically involved not only in learning and memory, but also during the activity-dependent developmental phases of neural circuit formation and refinement. Whether the mechanisms underlying LTP change during this phase of postnatal development, however, is unknown. We report here that, unlike LTP in the more mature CA1 region of the hippocampus, LTP in neonatal rodent hippocampus (<9 postnatal days,
View details for DOI 10.1038/nn985
View details for Web of Science ID 000180089300008
View details for PubMedID 12469130
Control of synaptic strength by glial TNF alpha
2002; 295 (5563): 2282-2285
Activity-dependent modulation of synaptic efficacy in the brain contributes to neural circuit development and experience-dependent plasticity. Although glia are affected by activity and ensheathe synapses, their influence on synaptic strength has largely been ignored. Here, we show that a protein produced by glia, tumor necrosis factor alpha (TNFalpha), enhances synaptic efficacy by increasing surface expression of AMPA receptors. Preventing the actions of endogenous TNFalpha has the opposite effects. Thus, the continual presence of TNFalpha is required for preservation of synaptic strength at excitatory synapses. Through its effects on AMPA receptor trafficking, TNFalpha may play roles in synaptic plasticity and modulating responses to neural injury.
View details for Web of Science ID 000174561700051
View details for PubMedID 11910117
RIM1 alpha is required for presynaptic long-term potentiation
2002; 415 (6869): 327-330
Two main forms of long-term potentiation (LTP)-a prominent model for the cellular mechanism of learning and memory-have been distinguished in the mammalian brain. One requires activation of postsynaptic NMDA (N-methyl d-aspartate) receptors, whereas the other, called mossy fibre LTP, has a principal presynaptic component. Mossy fibre LTP is expressed in hippocampal mossy fibre synapses, cerebellar parallel fibre synapses and corticothalamic synapses, where it apparently operates by a mechanism that requires activation of protein kinase A. Thus, presynaptic substrates of protein kinase A are probably essential in mediating this form of long-term synaptic plasticity. Studies of knockout mice have shown that the synaptic vesicle protein Rab3A is required for mossy fibre LTP, but the protein kinase A substrates rabphilin, synapsin I and synapsin II are dispensable. Here we report that mossy fibre LTP in the hippocampus and the cerebellum is abolished in mice lacking RIM1alpha, an active zone protein that binds to Rab3A and that is also a protein kinase A substrate. Our results indicate that the long-term increase in neurotransmitter release during mossy fibre LTP may be mediated by a unitary mechanism that involves the GTP-dependent interaction of Rab3A with RIM1alpha at the interface of synaptic vesicles and the active zone.
View details for Web of Science ID 000173293500045
View details for PubMedID 11797010
Regulation of synaptic strength by protein phosphatase 1
2001; 32 (6): 1133-1148
We investigated the role of postsynaptic protein phosphatase 1 (PP1) in regulating synaptic strength by loading CA1 pyramidal cells either with peptides that disrupt PP1 binding to synaptic targeting proteins or with active PP1. The peptides blocked synaptically evoked LTD but had no effect on basal synaptic currents mediated by either AMPA or NMDA receptors. They did, however, cause an increase in synaptic strength following the induction of LTD. Similarly, PP1 had no effect on basal synaptic strength but enhanced LTD. In cultured neurons, synaptic activation of NMDA receptors increased the proportion of PP1 localized to synapses. These results suggest that PP1 does not significantly regulate basal synaptic strength. Appropriate NMDA receptor activation, however, allows PP1 to gain access to synaptic substrates and be recruited to synapses where its activity is necessary for sustaining LTD.
View details for Web of Science ID 000172886800018
View details for PubMedID 11754843
Long-term depression in the nucleus accumbens: a neural correlate of behavioral sensitization to cocaine
2001; 4 (12): 1217-1223
A compelling model of experience-dependent plasticity is the long-lasting sensitization to the locomotor stimulatory effects of drugs of abuse. Adaptations in the nucleus accumbens (NAc), a component of the mesolimbic dopamine system, are thought to contribute to this behavioral change. Here we examine excitatory synaptic transmission in NAc slices prepared from animals displaying sensitization 10-14 days after repeated in vivo cocaine exposure. The ratio of AMPA (alpha-amino-3-hydroxy-5-methyl-4- isoxazole propionic acid) receptor- to NMDA (N-methyl-d-aspartate) receptor-mediated excitatory postsynaptic currents (EPSCs) was decreased at synapses made by prefrontal cortical afferents onto medium spiny neurons in the shell of the NAc. The amplitude of miniature EPSCs at these synapses also was decreased, as was the magnitude of long-term depression. These data suggest that chronic in vivo administration of cocaine elicits a long-lasting depression of excitatory synaptic transmission in the NAc, a change that may contribute to behavioral sensitization and addiction.
View details for Web of Science ID 000172525000018
View details for PubMedID 11694884
Long-term potentiation--a decade of progress?
1999; 285 (5435): 1870-1874
Long-term potentiation of synaptic transmission in the hippocampus is the leading experimental model for the synaptic changes that may underlie learning and memory. This review presents a current understanding of the molecular mechanisms of this long-lasting increase in synaptic strength and describes a simple model that unifies much of the data that previously were viewed as contradictory.
View details for PubMedID 10489359
Rapid redistribution of glutamate receptors contributes to long-term depression in hippocampal cultures
1999; 2 (5): 454-460
Synaptic strength can be altered by a variety of pre- or postsynaptic modifications. Here we test the hypothesis that long-term depression (LTD) involves a decrease in the number of glutamate receptors that are clustered at individual synapses in primary cultures of hippocampal neurons. Similar to a prominent form of LTD observed in hippocampal slices, LTD in hippocampal cultures required NMDA receptor activation and was accompanied by a decrease in the amplitude and frequency of miniature excitatory postsynaptic currents. Immunocytochemical analysis revealed that induction of LTD caused a concurrent decrease in the number of AMPA receptors clustered at synapses but had no effect on synaptic NMDA receptor clusters. These results suggest that a subtype-specific redistribution of synaptic glutamate receptors contributes to NMDA receptor-dependent LTD.
View details for Web of Science ID 000084609400016
View details for PubMedID 10321250
Rapid, activation-induced redistribution of ionotropic glutamate receptors in cultured hippocampal neurons
JOURNAL OF NEUROSCIENCE
1999; 19 (4): 1263-1272
We have examined the membrane localization of an AMPA receptor subunit (GluR1) and an NMDA receptor subunit (NR1) endogenously expressed in primary cultures of rat hippocampal neurons. In unstimulated cultures, both GluR1 and NR1 subunits were concentrated in SV2-positive synaptic clusters associated with dendritic shafts and spines. Within 5 min after the addition of 100 microM glutamate to the culture medium, a rapid and selective redistribution of GluR1 subunits away from a subset of synaptic sites was observed. This redistribution of GluR1 subunits was also induced by AMPA, did not require NMDA receptor activation, did not result from ligand-induced neurotoxicity, and was reversible after the removal of agonist. The activation-induced redistribution of GluR1 subunits was associated with a pronounced (approximately 50%) decrease in the frequency of miniature EPSCs, consistent with a role of GluR1 subunit redistribution in mediating rapid regulation of synaptic efficacy. We conclude that ionotropic glutamate receptors are regulated in native neurons by rapid, subtype-specific membrane trafficking, which may modulate synaptic transmission in response to physiological or pathophysiological activation.
View details for Web of Science ID 000078603500010
View details for PubMedID 9952404
- An immunocytochemical assay for activity-dependent redistribution of glutamate receptors from the postsynaptic plasma membrane MOLECULAR AND FUNCTIONAL DIVERSITY OF ION CHANNELS AND RECEPTORS 1999; 868: 550-553