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Heterosynaptic GABA Receptor Function within Feedforward Microcircuits Gates Glutamatergic Transmission in the Nucleus Accumbens Core.
Manz KM, Baxley AG, Zurawski Z, Hamm HE, Grueter BA
(2019) J Neurosci 39: 9277-9293
MeSH Terms: Animals, GABA-B Receptor Agonists, Glutamic Acid, Male, Mice, Mice, Inbred C57BL, Mice, Transgenic, Nerve Net, Nucleus Accumbens, Organ Culture Techniques, Receptors, GABA-B, Synapses, Synaptic Transmission
Show Abstract · Added March 24, 2020
Complex circuit interactions within the nucleus accumbens (NAc) facilitate goal-directed behavior. Medium spiny neurons (MSNs) mediate NAc output by projecting to functionally divergent brain regions, a property conferred, in part, by the differential projection patterns of D1- and D2 dopamine receptor-expressing MSNs. Glutamatergic afferents to the NAc direct MSN output by recruiting feedforward inhibitory microcircuits comprised of parvalbumin (PV)-expressing interneurons (INs). Furthermore, the GABA heteroreceptor (GABAR), a G-coupled G-protein-coupled receptor, is expressed at glutamatergic synapses throughout the mesolimbic network, yet its physiological context and synaptic mechanism within the NAc remains unknown. Here, we explored GABAR function at glutamatergic synapses within PV-IN-embedded microcircuits in the NAc core of male mice. We found that GABAR is expressed presynaptically and recruits a noncanonical signaling mechanism to reduce glutamatergic synaptic efficacy at D1(+) and D1(-) (putative D2) MSN subtypes. Furthermore, PV-INs, a robust source of neuronal GABA in the NAc, heterosynaptically target GABAR to selectively modulate glutamatergic transmission onto D1(+) MSNs. These findings elucidate a new mechanism of feedforward inhibition and refine mechanisms by which GABA heteroreceptors modulate mesolimbic circuit function. Glutamatergic transmission in the nucleus accumbens (NAc) critically contributes to goal-directed behaviors. However, intrinsic microcircuit mechanisms governing the integration of these synapses remain largely unknown. Here, we show that parvalbumin-expressing interneurons within feedforward microcircuits heterosynaptically target GABA heteroreceptors (GABAR) on glutamate terminals. Activation of presynaptically-expressed GABAR decreases glutamatergic synaptic strength by engaging a non-canonical signaling pathway that interferes with vesicular exocytotic release machinery. These findings offer mechanistic insight into the role of GABA heteroreceptors within reward circuitry, elucidate a novel arm to feedforward inhibitory networks, and inform the growing use of GABAR-selective pharmacotherapy for various motivational disorders, including addiction, major depressive disorder, and autism (Cousins et al., 2002; Kahn et al., 2009; Jacobson et al., 2018; Stoppel et al., 2018; Pisansky et al., 2019).
Copyright © 2019 the authors.
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13 MeSH Terms
Disabling Gβγ-SNAP-25 interaction in gene-targeted mice results in enhancement of long-term potentiation at Schaffer collateral-CA1 synapses in the hippocampus.
Irfan M, Zurawski Z, Hamm HE, Bark C, Stanton PK
(2019) Neuroreport 30: 695-699
MeSH Terms: Animals, Excitatory Postsynaptic Potentials, Hippocampus, Long-Term Potentiation, Mice, Transgenic, Neuronal Plasticity, Synapses, Synaptic Transmission, Synaptosomal-Associated Protein 25, Temporal Lobe
Show Abstract · Added March 24, 2020
Three SNARE proteins, SNAP-25, syntaxin 1A, and VAMP2 or synaptobrevin 2, constitute the minimal functional machinery needed for the regulated secretion of neurotransmitters. Dynamic changes in the regulated release of neurotransmitters are associated with the induction of long-term plasticity at central synapses. In-vitro studies have validated the C-terminus of SNAP-25 as a target for inhibitory Gi/o-coupled G-protein coupled receptors at a number of synapses. The physiological consequences of the interaction between Gi/o proteins and SNAP-25 in the context of activity-dependent long-term synaptic plasticity are not well understood. Here, we report direct ex-vivo evidence of the involvement of the C-terminus of SNAP-25 in inducing long-term potentiation of synaptic strength at Schaffer collateral-CA1 synapses using a gene-targeted mouse model with truncated C-terminus (carboxyl terminus) of SNAP-25. It has been shown previously that truncation of the three extreme C-terminal residues in SNAP-25[INCREMENT]3 homozygote mice reduces its interaction with the inhibitory Gβγ subunits two-fold. In in-vitro hippocampal slices, we show that these SNAP-25[INCREMENT]3 mice express significantly larger magnitude of long-term potentiation at hippocampal Schaffer collateral-CA1 synapses.
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10 MeSH Terms
The Elegance of Sonic Hedgehog: Emerging Novel Functions for a Classic Morphogen.
Garcia ADR, Han YG, Triplett JW, Farmer WT, Harwell CC, Ihrie RA
(2018) J Neurosci 38: 9338-9345
MeSH Terms: Animals, Hedgehog Proteins, Humans, Morphogenesis, Neural Stem Cells, Signal Transduction, Synapses
Show Abstract · Added April 10, 2019
Sonic Hedgehog (SHH) signaling has been most widely known for its role in specifying region and cell-type identity during embryonic morphogenesis. This mini-review accompanies a 2018 SFN mini-symposium that addresses an emerging body of research focused on understanding the diverse roles for Shh signaling in a wide range of contexts in neurodevelopment and, more recently, in the mature CNS. Such research shows that Shh affects the function of brain circuits, including the production and maintenance of diverse cell types and the establishment of wiring specificity. Here, we review these novel and unexpected functions and the unanswered questions regarding the role of SHH and its signaling pathway members in these cases.
Copyright © 2018 the authors 0270-6474/18/389338-08$15.00/0.
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7 MeSH Terms
Microglial Pruning of Synapses in the Prefrontal Cortex During Adolescence.
Mallya AP, Wang HD, Lee HNR, Deutch AY
(2019) Cereb Cortex 29: 1634-1643
MeSH Terms: Animals, Dendritic Spines, Female, Male, Microglia, Prefrontal Cortex, Pyramidal Cells, Rats, Sprague-Dawley, Synapses
Show Abstract · Added April 2, 2019
Exaggerated synaptic elimination in the prefrontal cortex (PFC) during adolescence has been suggested to contribute to the neuropathological changes of schizophrenia. Recent data indicate that microglia (MG) sculpt synapses during early postnatal development. However, it is not known if MG contribute to the structural maturation of the PFC, which has a protracted postnatal development. We determined if MG are involved in developmentally specific synapse elimination in the PFC, focusing on adolescence. Layer 5 PFC pyramidal cells (PCs) were intracellularly filled with Lucifer Yellow for dendritic spine measurements in postnatal day (P) 24, P30, P35, P39, and P50 rats. In the contralateral PFC we evaluated if MG engulfed presynaptic (glutamatergic) and postsynaptic (dendritic spines) elements. Dendritic spine density increased from P24 to P35, when spine density peaked. There was a significant increase in MG engulfment of spines at P39 relative to earlier ages; this subsided by P50. MG also phagocytosed presynaptic glutamatergic terminals. These data indicate that MG transiently prune synapses of PFC PCs during adolescence, when the symptoms of schizophrenia typically first appear. An increase in MG-mediated synaptic remodeling of PFC PCs may contribute to the structural changes observed in schizophrenia.
© The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.
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9 MeSH Terms
mGlu and mGlu modulate distinct excitatory inputs to the nucleus accumbens shell.
Turner BD, Rook JM, Lindsley CW, Conn PJ, Grueter BA
(2018) Neuropsychopharmacology 43: 2075-2082
MeSH Terms: Animals, Cocaine, Female, Mediodorsal Thalamic Nucleus, Mice, Mice, Inbred C57BL, Mice, Transgenic, Motor Activity, Neuronal Plasticity, Neurons, Nucleus Accumbens, Optogenetics, Oxazoles, Prefrontal Cortex, Pyridines, Receptor, Metabotropic Glutamate 5, Receptors, Metabotropic Glutamate, Synapses, Synaptic Transmission
Show Abstract · Added March 3, 2020
Glutamatergic transmission in the nucleus accumbens shell (NAcSh) is a substrate for reward learning and motivation. Metabotropic glutamate (mGlu) receptors regulate NAcSh synaptic strength by inducing long-term depression (LTD). Inputs from prefrontal cortex (PFC) and medio-dorsal thalamus (MDT) drive opposing motivated behaviors yet mGlu receptor regulation of these synapses is unexplored. We examined Group I mGlu receptor regulation of PFC and MDT glutamatergic synapses onto specific populations of NAc medium spiny neurons (MSNs) using D1tdTom BAC transgenic mice and optogenetics. Synaptically evoked long-term depression (LTD) at MDT-NAcSh synapses required mGlu but not mGlu and was specific for D1(+) MSNs, whereas PFC LTD was expressed at both D1(+) and D1(-) MSNs and required mGlu but not mGlu. Two weeks after five daily non-contingent cocaine exposures (15 mg/kg), LTD was attenuated at MDT-D1(+) synapses but was rescued by the mGlu5-positive allosteric modulator (PAM) VU0409551. These results highlight unique plasticity mechanisms regulating specific NAcSh synapses.
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MeSH Terms
Excitatory Synaptic Input to Hilar Mossy Cells under Basal and Hyperexcitable Conditions.
Hedrick TP, Nobis WP, Foote KM, Ishii T, Chetkovich DM, Swanson GT
(2017) eNeuro 4:
MeSH Terms: Animals, CA3 Region, Hippocampal, Excitatory Postsynaptic Potentials, Female, Male, Mice, Mice, Inbred C57BL, Mossy Fibers, Hippocampal, Neural Pathways, Neuronal Plasticity, Organ Culture Techniques, Pyramidal Cells, Synapses, Synaptic Transmission
Show Abstract · Added April 2, 2019
Hilar mossy cells (HMCs) in the hippocampus receive glutamatergic input from dentate granule cells (DGCs) via mossy fibers (MFs) and back-projections from CA3 pyramidal neuron collateral axons. Many fundamental features of these excitatory synapses have not been characterized in detail despite their potential relevance to hippocampal cognitive processing and epilepsy-induced adaptations in circuit excitability. In this study, we compared pre- and postsynaptic parameters between MF and CA3 inputs to HMCs in young and adult mice of either sex and determined the relative contributions of the respective excitatory inputs during and models of hippocampal hyperexcitability. The two types of excitatory synapses both exhibited a modest degree of short-term plasticity, with MF inputs to HMCs exhibiting lower paired-pulse (PP) and frequency facilitation than was described previously for MF-CA3 pyramidal cell synapses. MF-HMC synapses exhibited unitary excitatory synaptic currents (EPSCs) of larger amplitude, contained postsynaptic kainate receptors, and had a lower NMDA/AMPA receptor ratio compared to CA3-HMC synapses. Pharmacological induction of hippocampal hyperexcitability transformed the abundant but relatively weak CA3-HMC connections to very large amplitude spontaneous bursts of compound EPSCs (cEPSCs) in young mice (∼P20) and, to a lesser degree, in adult mice (∼P70). CA3-HMC cEPSCs were also observed in slices prepared from mice with spontaneous seizures several weeks after intrahippocampal kainate injection. Strong excitation of HMCs during synchronous CA3 activity represents an avenue of significant excitatory network generation back to DGCs and might be important in generating epileptic networks.
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MeSH Terms
Noise-induced cochlear synaptopathy in rhesus monkeys (Macaca mulatta).
Valero MD, Burton JA, Hauser SN, Hackett TA, Ramachandran R, Liberman MC
(2017) Hear Res 353: 213-223
MeSH Terms: Animals, Auditory Fatigue, Auditory Threshold, Cochlea, Cochlear Diseases, Disease Models, Animal, Evoked Potentials, Auditory, Brain Stem, Hair Cells, Auditory, Hearing, Hearing Loss, Noise-Induced, Macaca mulatta, Noise, Otoacoustic Emissions, Spontaneous, Synapses, Synaptic Transmission, Time Factors
Show Abstract · Added April 3, 2018
Cochlear synaptopathy can result from various insults, including acoustic trauma, aging, ototoxicity, or chronic conductive hearing loss. For example, moderate noise exposure in mice can destroy up to ∼50% of synapses between auditory nerve fibers (ANFs) and inner hair cells (IHCs) without affecting outer hair cells (OHCs) or thresholds, because the synaptopathy occurs first in high-threshold ANFs. However, the fiber loss likely impairs temporal processing and hearing-in-noise, a classic complaint of those with sensorineural hearing loss. Non-human primates appear to be less vulnerable to noise-induced hair-cell loss than rodents, but their susceptibility to synaptopathy has not been studied. Because establishing a non-human primate model may be important in the development of diagnostics and therapeutics, we examined cochlear innervation and the damaging effects of acoustic overexposure in young adult rhesus macaques. Anesthetized animals were exposed bilaterally to narrow-band noise centered at 2 kHz at various sound-pressure levels for 4 h. Cochlear function was assayed for up to 8 weeks following exposure via auditory brainstem responses (ABRs) and otoacoustic emissions (OAEs). A moderate loss of synaptic connections (mean of 12-27% in the basal half of the cochlea) followed temporary threshold shifts (TTS), despite minimal hair-cell loss. A dramatic loss of synapses (mean of 50-75% in the basal half of the cochlea) was seen on IHCs surviving noise exposures that produced permanent threshold shifts (PTS) and widespread hair-cell loss. Higher noise levels were required to produce PTS in macaques compared to rodents, suggesting that primates are less vulnerable to hair-cell loss. However, the phenomenon of noise-induced cochlear synaptopathy in primates is similar to that seen in rodents.
Copyright © 2017 Elsevier B.V. All rights reserved.
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16 MeSH Terms
A Presynaptic Group III mGluR Recruits Gβγ/SNARE Interactions to Inhibit Synaptic Transmission by Cone Photoreceptors in the Vertebrate Retina.
Van Hook MJ, Babai N, Zurawski Z, Yim YY, Hamm HE, Thoreson WB
(2017) J Neurosci 37: 4618-4634
MeSH Terms: Ambystoma, Animals, Excitatory Postsynaptic Potentials, Female, GTP-Binding Protein beta Subunits, GTP-Binding Protein gamma Subunits, Male, Receptors, Metabotropic Glutamate, Retinal Cone Photoreceptor Cells, Retinal Horizontal Cells, SNARE Proteins, Synapses, Synaptic Transmission
Show Abstract · Added March 24, 2020
G-protein βγ subunits (Gβγ) interact with presynaptic proteins and regulate neurotransmitter release downstream of Ca influx. To accomplish their roles in sensory signaling, photoreceptor synapses use specialized presynaptic proteins that support neurotransmission at active zone structures known as ribbons. While several G-protein coupled receptors (GPCRs) influence synaptic transmission at ribbon synapses of cones and other retinal neurons, it is unknown whether Gβγ contributes to these effects. We tested whether activation of one particular GPCR, a metabotropic glutamate receptor (mGluR), can reduce cone synaptic transmission via Gβγ in tiger salamander retinas. In recordings from horizontal cells, we found that an mGluR agonist (L-AP4) reduced cone-driven light responses and mEPSC frequency. In paired recordings of cones and horizontal cells, L-AP4 slightly reduced cone I (∼10%) and caused a larger reduction in cone-driven EPSCs (∼30%). Proximity ligation assay revealed direct interactions between SNAP-25 and Gβγ subunits in retinal synaptic layers. Pretreatment with the SNAP-25 cleaving protease BoNT/A inhibited L-AP4 effects on synaptic transmission, as did introduction of a peptide derived from the SNAP-25 C terminus. Introducing Gβγ subunits directly into cones reduced EPSC amplitude. This effect was inhibited by BoNT/A, supporting a role for Gβγ/SNAP-25 interactions. However, the mGluR-dependent reduction in I was not mimicked by Gβγ, indicating that this effect was independent of Gβγ. The finding that synaptic transmission at cone ribbon synapses is regulated by Gβγ/SNAP-25 interactions indicates that these mechanisms are shared by conventional and ribbon-type synapses. Gβγ liberated from other photoreceptor GPCRs is also likely to regulate synaptic transmission. Dynamic regulation of synaptic transmission by presynaptic G-protein coupled receptors shapes information flow through neural circuits. At the first synapse in the visual system, presynaptic metabotropic glutamate receptors (mGluRs) regulate cone photoreceptor synaptic transmission, although the mechanisms and functional impact of this are unclear. We show that mGluRs regulate light response encoding across the cone synapse, accomplished in part by triggering G-protein βγ subunits (Gβγ) interactions with SNAP-25, a core component of the synaptic vesicle fusion machinery. In addition to revealing a role in visual processing, this provides the first demonstration that Gβγ/SNAP-25 interactions regulate synaptic function at a ribbon-type synapse, contributing to an emerging picture of the ubiquity of Gβγ/SNARE interactions in regulating synaptic transmission throughout the nervous system.
Copyright © 2017 the authors 0270-6474/17/374619-17$15.00/0.
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MeSH Terms
Densin-180 Controls the Trafficking and Signaling of L-Type Voltage-Gated Ca1.2 Ca Channels at Excitatory Synapses.
Wang S, Stanika RI, Wang X, Hagen J, Kennedy MB, Obermair GJ, Colbran RJ, Lee A
(2017) J Neurosci 37: 4679-4691
MeSH Terms: Animals, Calcium Channels, L-Type, Calcium Signaling, Cerebral Cortex, Excitatory Postsynaptic Potentials, Ion Channel Gating, Male, Mice, Mice, Inbred C57BL, Mice, Knockout, Neurons, Protein Transport, Sialoglycoproteins, Signal Transduction, Synapses
Show Abstract · Added April 26, 2017
Voltage-gated Ca1.2 and Ca1.3 (L-type) Ca channels regulate neuronal excitability, synaptic plasticity, and learning and memory. Densin-180 (densin) is an excitatory synaptic protein that promotes Ca-dependent facilitation of voltage-gated Ca1.3 Ca channels in transfected cells. Mice lacking densin (densin KO) exhibit defects in synaptic plasticity, spatial memory, and increased anxiety-related behaviors-phenotypes that more closely match those in mice lacking Ca1.2 than Ca1.3. Therefore, we investigated the functional impact of densin on Ca1.2. We report that densin is an essential regulator of Ca1.2 in neurons, but has distinct modulatory effects compared with its regulation of Ca1.3. Densin binds to the N-terminal domain of Ca1.2, but not that of Ca1.3, and increases Ca1.2 currents in transfected cells and in neurons. In transfected cells, densin accelerates the forward trafficking of Ca1.2 channels without affecting their endocytosis. Consistent with a role for densin in increasing the number of postsynaptic Ca1.2 channels, overexpression of densin increases the clustering of Ca1.2 in dendrites of hippocampal neurons in culture. Compared with wild-type mice, the cell surface levels of Ca1.2 in the brain, as well as Ca1.2 current density and signaling to the nucleus, are reduced in neurons from densin KO mice. We conclude that densin is an essential regulator of neuronal Ca1 channels and ensures efficient Ca1.2 Ca signaling at excitatory synapses. The number and localization of voltage-gated Ca Ca channels are crucial determinants of neuronal excitability and synaptic transmission. We report that the protein densin-180 is highly enriched at excitatory synapses in the brain and enhances the cell surface trafficking and postsynaptic localization of Ca1.2 L-type Ca channels in neurons. This interaction promotes coupling of Ca1.2 channels to activity-dependent gene transcription. Our results reveal a mechanism that may contribute to the roles of Ca1.2 in regulating cognition and mood.
Copyright © 2017 the authors 0270-6474/17/374679-13$15.00/0.
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15 MeSH Terms
Endocannabinoid signalling modulates susceptibility to traumatic stress exposure.
Bluett RJ, Báldi R, Haymer A, Gaulden AD, Hartley ND, Parrish WP, Baechle J, Marcus DJ, Mardam-Bey R, Shonesy BC, Uddin MJ, Marnett LJ, Mackie K, Colbran RJ, Winder DG, Patel S
(2017) Nat Commun 8: 14782
MeSH Terms: Amygdala, Animals, Anxiety, Arachidonic Acids, Behavior, Animal, Benzodioxoles, Disease Susceptibility, Dronabinol, Endocannabinoids, Excitatory Postsynaptic Potentials, Female, Glutamates, Glycerides, Hippocampus, Lipoprotein Lipase, Male, Mice, Inbred ICR, Mice, Knockout, Phenotype, Piperidines, Resilience, Psychological, Signal Transduction, Stress, Psychological, Synapses
Show Abstract · Added April 7, 2017
Stress is a ubiquitous risk factor for the exacerbation and development of affective disorders including major depression and posttraumatic stress disorder. Understanding the neurobiological mechanisms conferring resilience to the adverse consequences of stress could have broad implications for the treatment and prevention of mood and anxiety disorders. We utilize laboratory mice and their innate inter-individual differences in stress-susceptibility to demonstrate a critical role for the endogenous cannabinoid 2-arachidonoylglycerol (2-AG) in stress-resilience. Specifically, systemic 2-AG augmentation is associated with a stress-resilient phenotype and enhances resilience in previously susceptible mice, while systemic 2-AG depletion or CB1 receptor blockade increases susceptibility in previously resilient mice. Moreover, stress-resilience is associated with increased phasic 2-AG-mediated synaptic suppression at ventral hippocampal-amygdala glutamatergic synapses and amygdala-specific 2-AG depletion impairs successful adaptation to repeated stress. These data indicate amygdala 2-AG signalling mechanisms promote resilience to adverse effects of acute traumatic stress and facilitate adaptation to repeated stress exposure.
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24 MeSH Terms