GABA Release Research Articles

Target-specific control of olfactory bulb periglomerular cells by GABAergic and cholinergic basal forebrain inputs.

The olfactory bulb (OB), the first relay for odor processing in the brain, receives dense GABAergic and cholinergic long-range projections from basal forebrain (BF) nuclei that provide information about the internal state and behavioral context of the animal. However, the targets, impact, and dynamic of these afferents are still unclear. How BF synaptic inputs modulate activity in diverse subtypes of periglomerular (PG) interneurons using optogenetic stimulation and loose cell-attached or whole-cell patch-clamp recording in OB slices from adult mice were studied in this article. GABAergic BF inputs potently blocked PG cells firing except in a minority of calretinin-expressing cells in which GABA release elicited spiking. Parallel cholinergic projections excited a previously overlooked PG cell subtype via synaptic activation of M1 muscarinic receptors. Low-frequency stimulation of the cholinergic axons drove persistent firing in these PG cells, thereby increasing tonic inhibition in principal neurons. Taken together, these findings suggest that modality-specific BF inputs can orchestrate synaptic inhibition in OB glomeruli using multiple, potentially independent, inhibitory or excitatory target-specific pathways.

Lower Levels of GABAergic Function Markers in Corticotropin-Releasing Hormone-Expressing Neurons in the sgACC of Human Subjects With Depression

RationaleA previous transcriptome meta-analysis revealed significantly lower levels of corticotropin-releasing hormone (CRH) mRNA in corticolimbic brain regions in major depressive disorder (MDD) subjects, suggesting that cortical CRH-expressing (CRH+) cells are affected in MDD. Rodent studies show that cortical CRH is mostly expressed in GABAergic interneurons; however, the characteristic features of CRH+ cells in human brain cortex and their association with MDD are largely unknown.MethodsSubgenual anterior cingulate cortex (sgACC) of human subjects without brain disorders were labeled using fluorescent in situ hybridization (FISH) for CRH and markers of excitatory (SLC17A7), inhibitory (GAD1) neurons, as well as markers of other interneuron subpopulations (PVALB, SST, VIP). MDD-associated changes in CRH+ cell density and cellular CRH expression (n = 6/group) were analyzed. RNA-sequencing was performed on sgACC CRH+ interneurons from comparison and MDD subjects (n = 6/group), and analyzed for group differences. The effect of reduced BDNF on CRH expression was tested in mice with blocked TrkB function.ResultsAbout 80% of CRH+ cells were GABAergic and 17.5% were glutamatergic. CRH+ GABAergic interneurons co-expressed VIP (52%), SST (7%), or PVALB (7%). MDD subjects displayed lower CRH mRNA levels in GABAergic interneurons relative to comparison subjects without changes in cell density. CRH+ interneurons show transcriptomic profile suggesting lower excitability and less GABA release and reuptake. Further analyses suggested that these molecular changes are not mediated by altered glucocorticoid feedback and potentially occur downstream for a common modulator of neurotrophic function.SummaryCRH+ cells in human sgACC are a heterogeneous population of GABAergic interneurons, although largely co-expressing VIP. Our data suggest that MDD is associated with reduced markers of inhibitory function in sgACC CRH+ interneurons, and provide further evidence for impaired GABAergic function in the cortex in MDD.

A conditional GABAergic synaptic vesicle marker for Drosophila

BackgroundThroughout the animal kingdom, GABA is the principal inhibitory neurotransmitter of the nervous system. It is essential for maintaining the homeostatic balance between excitation and inhibition required for the brain to operate normally. Identification of GABAergic neurons and their GABA release sites are thus essential for understanding how the brain regulates the excitability of neurons and the activity of neural circuits responsible for numerous aspects of brain function including information processing, locomotion, learning, memory, and synaptic plasticity, among others. New methodSince the structure and features of GABA synapses are critical to understanding their function within specific neural circuits of interest, here we developed and characterized a conditional marker of GABAergic synaptic vesicles for Drosophila, 9XV5-vGAT. Results9XV5-vGAT is validated for conditionality of expression, specificity for localization to synaptic vesicles, specificity for expression in GABAergic neurons, and functionality. Its utility for GABAergic neurotransmitter phenotyping and identification of GABA release sites was verified for ellipsoid body neurons of the central complex. In combination with previously reported conditional SV markers for acetylcholine and glutamate, 9XV5-vGAT was used to demonstrate fast neurotransmitter phenotyping of subesophageal ganglion neurons. Comparison with existing methodsThis method is an alternative to single cell transcriptomics for neurotransmitter phenotyping and can be applied to any neurons of interest represented by a binary transcription system driver. ConclusionA conditional GABAergic synaptic vesicle marker has been developed and validated for GABA neurotransmitter phenotyping and subcellular localization of GABAergic synaptic vesicles.

5-HT3A receptors maintain hippocampal LTP in a CB1 and GABAA receptor- dependent manner for spatial memory.

As the only ionotropic receptor in the 5-HT receptor family, the 5-HT3 receptor (5-HT3 R) is involved in psychiatric disorders and its modulators have potential therapeutic effects for cognitive impairment in these disorders. However, it remains unclear how 5-HT3 Rs shape synaptic plasticity for memory function. Extracellular as well as whole-cell electrophysiological recordings were used to monitor hippocampal LTP and synaptic transmission in hippocampal slices in 5-HT3 AR knockout or 5-HT3 AR-GFP mice. Immunocytochemistry, qRT-PCR and western blotting were used to measure receptor expression. We also assessed hippocampal dependent cognition and memory, using the Morris water maze (MWM) and novel object recognition. We found that 5-HT3 R dysfunction impaired hippocampal LTP in Schaffer collateral (SC)-CA1 pathway in hippocampal slices, by facilitating GABAergic inputs in pyramidal cells. This effect was dependent on 5-HT3 Rs on axon terminals. It resulted from reduced expression and function of the cannabinoid receptor 1 (CB1 R) co-localized with 5-HT3 Rs on axon terminals, and then led to diminishment of tonic inhibition of GABA release by CB1 Rs. Inhibition of CB1 Rs mimicked the facilitation of GABAergic transmission by 5-HT3 R disruption. Consequently, mice with hippocampal 5-HT3 R disruption exhibited impaired spatial memory in MWM tasks. These results suggest that 5-HT3 Rs are crucial in enabling hippocampal synaptic plasticity via a novel CB1 R-GABAA -dependent pathway to regulate spatial memory.

Silencing of Hippocampal Somatostatin Interneurons Induces Recurrent Spontaneous Limbic Seizures in Mice

The hippocampus proper and the subiculum contain two major populations of somatostatin (SST)-containing interneurons, oriens-lacunosum moleculare (O-LM) cells projecting from the stratum oriens to the stratum lacunosum moleculare and bistratified cells with their cell bodies close to the pyramidal cell layer and axons terminating in the strata radiatum and oriens. Both types of interneurons innervate pyramidal cell dendrites and exert prominent feedback inhibition. We now investigated whether impairing this type of feed-back inhibition by selectively inhibiting GABA release from SST expressing interneurons in hippocampal sector CA1 and subiculum may be sufficient to induce spontaneous recurrent seizures. We injected transgenic mice expressing Cre-recombinase on the SST promoter unilaterally into the ventral CA1 sector and subiculum with an adeno-associated viral (AAV) vector expressing tetanus toxin light chain (TeLC) with its reading frame inverted in a flip-excision (FLEX) cassette. This treatment resulted in specific expression of TeLC and silencing of SST-containing interneurons. We continuously monitored the EEG and behavior of the mice for six weeks. Nine out of eleven mice within 10 days developed series of pre- or interictal spikes (IS, 21.4 ± 6.83 per week) and four mice exposed recurrent spontaneous seizures (SRS, 1.5 ± 0.29 per week). All 23 SRS observed were preceded by IS series. Our data demonstrate a critical role of feed-forward inhibition mediated by SST-containing interneurons suggesting that their sustained malfunctioning can be causatively involved in the development of TLE.

Postpartum State, but Not Maternal Caregiving or Level of Anxiety, Increases Medial Prefrontal Cortex GAD65 and vGAT in Female Rats.

Upregulation of the inhibitory neurotransmitter, GABA, is involved in many of the behavioral differences between postpartum and nulliparous female rodents. This is evidenced by studies showing that pharmacological blockade of GABAergic activity impairs maternal caregiving and postpartum affective behaviors. However, the influence of motherhood on the capacity for GABA synthesis or release in the medial prefrontal cortex (mPFC; brain region involved in many social and affective behaviors) is not well-understood. Western blotting was used to compare postpartum and nulliparous rats in protein levels of the 65-kD isoform of glutamic acid decarboxylase (GAD65; synthesizes most GABA released from terminals) and vesicular GABA transporter (vGAT; accumulates GABA into synaptic vesicles for release) in the mPFC. We found that postpartum mothers had higher GAD65 and vGAT compared to virgins, but such differences were not found between maternally sensitized and non-sensitized virgins, indicating that reproduction rather than just the display of maternal caregiving is required. To test whether GAD65 and vGAT levels in the mPFC were more specifically related to anxiety-related behavior within postpartum mothers, we selected 8 low-anxiety and 8 high-anxiety dams based on their time spent in the open arms of an elevated plus maze on postpartum day 7. There were no significant differences between the anxiety groups in either GAD65 or vGAT levels. These data further indicate that frontal cortical GABA is affected by female reproduction and more likely contributes to differences in the display of socioemotional behaviors across, but not within, female reproductive state.

Mice with monoallelic GNAO1 loss exhibit reduced inhibitory synaptic input to cerebellar Purkinje cells.

GNAO1 encodes Gαo, a heterotrimeric G protein α subunit in the Gi/o family. In this report, we used a Gnao1 mouse model "G203R" previously described as a "gain-of-function" Gnao1 mutant with movement abnormalities and enhanced seizure susceptibility. Here, we report an unexpected second mutation resulting in a loss-of-function Gαo protein, and describe alterations in central synaptic transmission. Whole cell patch clamp recordings from Purkinje cells (PCs) in acute cerebellar slices from Gnao1 mutant mice showed significantly lower frequencies of spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs) compared with WT mice. There was no significant change in sEPSCs or mEPSCs. Whereas mIPSC frequency was reduced, mIPSC amplitudes were not affected, suggesting a presynaptic mechanism of action. A modest decrease in the number of molecular layer interneurons was insufficient to explain the magnitude of IPSC suppression. Paradoxically, Gi/o inhibitors (pertussis toxin) enhanced the mutant-suppressed mIPSC frequency and eliminated the difference between WT and Gnao1 mice. Although GABAB receptor regulates mIPSCs, neither agonists nor antagonists of this receptor altered function in the mutant mouse PCs. This study is an electrophysiological investigation of the role of Gi/o protein in cerebellar synaptic transmission using an animal model with a loss-of-function Gi/o protein.NEW & NOTEWORTHY This report reveals the electrophysiological mechanisms of a movement disorder animal model with monoallelic Gnao1 loss. This study illustrates the role of Gαo protein in regulating GABA release in mouse cerebellum. This study could also facilitate the discovery of new drugs or drug repurposing for GNAO1-associated disorders. Moreover, since GNAO1 shares pathways with other genes related to movement disorders, developing drugs for the treatment of GNAO1-associated movement disorders could further the pharmacological intervention for other monogenic movement disorders.

Differential target multiplexed spinal cord stimulation programming modulates proteins involved in ion regulation in an animal model of neuropathic pain.

The effect of spinal cord stimulation (SCS) using differential target multiplexed programming (DTMP) on proteins involved in the regulation of ion transport in spinal cord (SC) tissue of an animal model of neuropathic pain was evaluated in comparison to low rate (LR) SCS. Rats subjected to the spared nerve injury model (SNI) and implanted with a SCS lead were assigned to DTMP or LR and stimulated for 48 h. A No-SCS group received no stimulation, and a Sham group received no SNI or stimulation. Proteins in the dorsal ipsilateral quadrant of the stimulated SC were identified and quantified using mass spectrometry. Proteins significantly modulated by DTMP or LR relative to No-SCS were identified. Bioinformatic tools were used to identify proteins related to ion transport regulation. DTMP modulated a larger number of proteins than LR. More than 40 proteins significantly involved in the regulation of chloride (Cl−), potassium (K+), sodium (Na+), or calcium (Ca2+) ions were identified. SNI affected proteins that promote the increase of intracellular Ca2+, Na+, and K+ and decrease of intracellular Cl−. DTMP modulated proteins involved in glial response to neural injury that affect Ca2+ signaling. DTMP decreased levels of proteins related to Ca2+ transport that may result in the reduction of intracellular Ca2+. Presynaptic proteins involved in GABA vesicle formation and release were upregulated by DTMP. DTMP also upregulated postsynaptic proteins involved with elevated intracellular Cl−, while modulating proteins, expressed by astrocytes, that regulate postsynaptic Cl− inhibition. DTMP downregulated K+ regulatory proteins affected by SNI that affect neuronal depolarization, and upregulated proteins that are associated with a decrease of intracellular neuronal K+ and astrocyte uptake of extracellular K+. DTMP treatment modulated the expression of proteins with the potential to facilitate a reversal of dysregulation of ion transport and signaling associated with a model of neuropathic pain.

Proteomics Study Reveals the Anti-Depressive Mechanisms and the Compatibility Advantage of Chaihu-Shugan-San in a Rat Model of Chronic Unpredictable Mild Stress

Background: Chaihu-Shugan-San is a classical prescription to treat depression. According to the traditional Chinese medicine (TCM) principle, the 2 decomposed recipes in Chaihu-Shugan-San exert synergistic effects, including Shu Gan (stagnated Gan-Qi dispersion) and Rou Gan (Gan nourishment to alleviate pain). However, the specific mechanism of Chaihu-Shugan-San on depression and its compatibility rule remain to be explored. Objective: We aimed to explore the anti-depression mechanisms and analyze the advantage of TCM compatibility of Chaihu-Shugan-San. Methods: The chronic unpredictable mild stress (CUMS) rat model was established. Antidepressant effects were evaluated by sucrose preference test (SPT), and forced swimming test (FST). Tandem Mass Tag (TMT)-based quantitative proteomics of the hippocampus was used to obtain differentially expressed proteins (DEPs). Bioinformatics analysis including Gene Ontology (GO), pathway enrichment, and protein-protein interaction (PPI) networks was utilized to study the DEPs connections. At last, the achieved key targets were verified by western blotting. Results: Chaihu-Shugan-San increased weight gain and food intake, as well as exhibited better therapeutic effects including enhanced sucrose preference and extended immobility time when compared with its decomposed recipes. Proteomics showed Chaihu-Shugan-San, Shu Gan, and Rou Gan regulated 110, 12, and 407 DEPs, respectively. Compared with Shu Gan or Rou Gan alone, the expression of 22 proteins was additionally changed by Chaihu-Shugan-San treatment, whereas the expression of 323 proteins whose expression was changed by Shu Gan or Rou Gan alone were not changed by Chaihu-Shugan-San treatment. Bioinformatics analysis demonstrated that Chaihu-Shugan-San affected neurotransmitter’s release and transmission cycle (e.g., γ-aminobutyric acid (GABA), glutamate, serotonin, norepinephrine, dopamine, and acetylcholine). GABA release pathway is also targeted by the 22 DEPs. Unexpectedly, only 2 pathways were enriched by the 323 DEPs: Metabolism and Cellular responses to external stimuli. Lastly, the expression of Gad2, Vamp2, and Pde2a was verified by western blotting. Conclusions: Chaihu-Shugan-San treats depression via multiple targets and pathways, which may include regulations of 110 DEPs and some neurotransmitter’s transmission cycle. Compared with Shu Gan and Rou Gan, the 22 Chaihu-Shugan-San advanced proteins and the affected GABA pathway may be the advantages of Chaihu-Shugan-San compatibility. This research offers data and theory support for the clinical application of Chaihu-Shugan-San.

Presynaptic GABAB receptors differentially modulate GABA release from cholecystokinin and parvalbumin interneurons onto CA1 pyramidal neurons: A cell type-specific labeling and activating study

Combining cell type-specific optogenetics and whole cell recordings on mouse acute hippocampal slices, we compared GABA release from cholecystokinin-expressing (CCK) and parvalbumin-expressing (PV) interneurons onto CA1 pyramidal neurons. Baclofen, a selective GABAB receptor agonist, inhibited GABAergic synaptic transmission greater from CCK terminals, compared to that from PV terminals. The N-type calcium channels on CCK and P/Q-type calcium channels on PV terminals contributed to the GABAB receptor-mediated inhibition, respectively. Our data thus provide direct evidence that GABAB receptors differentially modulate GABA release from CCK and PV interneurons, adding to an increasing list of differences between these two interneuron subtypes in modulating hippocampal pyramidal neurons.

Critical Role of Astrocytic Polyamine and GABA Metabolism in Epileptogenesis.

Accumulating evidence indicate that astrocytes are essential players of the excitatory and inhibitory signaling during normal and epileptiform activity via uptake and release of gliotransmitters, ions, and other substances. Polyamines can be regarded as gliotransmitters since they are almost exclusively stored in astrocytes and can be released by various mechanisms. The polyamine putrescine (PUT) is utilized to synthesize GABA, which can also be released from astrocytes and provide tonic inhibition on neurons. The polyamine spermine (SPM), synthesized form PUT through spermidine (SPD), is known to unblock astrocytic Cx43 gap junction channels and therefore facilitate astrocytic synchronization. In addition, SPM released from astrocytes may also modulate neuronal NMDA, AMPA, and kainate receptors. As a consequence, astrocytic polyamines possess the capability to significantly modulate epileptiform activity. In this study, we investigated different steps in polyamine metabolism and coupled GABA release to assess their potential to control seizure generation and maintenance in two different epilepsy models: the low-[Mg2+] model of temporal lobe epilepsy in vitro and in the WAG/Rij rat model of absence epilepsy in vivo. We show that SPM is a gliotransmitter that is released from astrocytes and significantly contributes to network excitation. Importantly, we found that inhibition of SPD synthesis completely prevented seizure generation in WAG/Rij rats. We hypothesize that this antiepileptic effect is attributed to the subsequent enhancement of PUT to GABA conversion in astrocytes, leading to GABA release through GAT-2/3 transporters. This interpretation is supported by the observation that antiepileptic potential of the Food and Drug Administration (FDA)-approved drug levetiracetam can be diminished by specifically blocking astrocytic GAT-2/3 with SNAP-5114, suggesting that levetiracetam exerts its effect by increasing surface expression of GAT-2/3. Our findings conclusively suggest that the major pathway through which astrocytic polyamines contribute to epileptiform activity is the production of GABA. Modulation of astrocytic polyamine levels, therefore, may serve for a more effective antiepileptic drug development in the future.

Clinical Pharmacology of Levetiracetam in Infants and Children

Levetiracetam inhibits focal and secondary generalized tonic-clonic seizures. The mechanism of levetiracetam action is not fully understood, however the correlation between binding affinity of levetiracetam and its analogues and their potency toward audiogenic seizures suggest that the synaptic vesicle glycoprotein 2A mediates the anticonvulsant effects of levetiracetam. The neural function of the synaptic vesicle 2A protein is not fully understood, but binding of levetiracetam to synaptic vesicle glycoprotein 2A might affect neuronal excitability by modifying the release of glutamate GABA through an action on vesicular function. Synaptic vesicle glycoprotein 2A may plain a role in vesicle recycling following exocytosis of neurotransmitter. In addition, levetiracetam inhibits N-type Ca2+ channels and Ca2+ release from intracellular stores. Levetiracetam may be administered intravenously or orally to infants and children and in children the levetiracetam dose varies according to the child age and body-weight. Levetiracetam is almost completed absorbed after oral administration and levetiracetam is found efficacy and safe in infants and children but it may induce adverse-effects. The levetiracetam elimination half-life is about 6 hours in infants and children, and in children the renal clearance is similar to the non-renal clearance. The prophylaxis, treatment, and trials with levetiracetam have been extensively studied in infants and children. Levetiracetam freely crosses the human placenta and freely migrates into the breast-milk. The aim of this study is to review the levetiracetam dosing, efficacy, safety, adverse-effects, pharmacokinetics, prophylaxis, treatment, and trials and transfer of levetiracetam across the human placenta and levetiracetam migration into the breast-milk.

Alcohol dependence and withdrawal increase sensitivity of central amygdalar GABAergic synapses to the glucocorticoid receptor antagonist mifepristone in male rats

Aberrant glucocorticoid signaling via glucocorticoid receptors (GR) plays a critical role in alcohol use disorder (AUD). Acute alcohol withdrawal and protracted abstinence in dependent rats are associated with increased GR signaling and changes in GR-mediated transcriptional activity in the rat central nucleus of the amygdala (CeA). The GR antagonist mifepristone decreases alcohol consumption in dependent rats during acute withdrawal and protracted abstinence. Regulation of CeA synaptic activity by GR is currently unknown. Here, we utilized mifepristone and the selective GR antagonist CORT118335 (both at 10 μM) as pharmacological tools to dissect the role of GR on GABA transmission in male, adult Sprague-Dawley rats using slice electrophysiology. We subjected rats to chronic intermittent alcohol vapor exposure for 5–7 weeks to induce alcohol dependence. A subset of dependent rats subsequently underwent protracted alcohol withdrawal for 2 weeks, and air-exposed rats served as controls. Mifepristone reduced the frequency of pharmacologically-isolated spontaneous inhibitory postsynaptic currents (sIPSC) in the CeA (medial subdivision) without affecting postsynaptic measures in all groups, suggesting decreased GABA release with the largest effect in dependent rats. CORT118335 did not significantly alter GABA transmission in naïve, but decreased sIPSC frequency in dependent rats. Similarly, mifepristone decreased amplitudes of evoked inhibitory postsynaptic potentials only in dependent rats and during protracted withdrawal. Collectively, our study provides insight into regulation of CeA GABAergic synapses by GR. Chronic ethanol enhances the efficiency of mifepristone and CORT118335, thus highlighting the potential of drugs targeting GR as a promising pharmacological avenue for the treatment of AUD.

Dopamine D2L Receptor Deficiency Alters Neuronal Excitability and Spine Formation in Mouse Striatum.

The striatum contains several types of neurons including medium spiny projection neurons (MSNs), cholinergic interneurons (ChIs), and fast-spiking interneurons (FSIs). Modulating the activity of these neurons by the dopamine D2 receptor (D2R) can greatly impact motor control and movement disorders. D2R exists in two isoforms: D2L and D2S. Here, we assessed whether alterations in the D2L and D2S expression levels affect neuronal excitability and synaptic function in striatal neurons. We observed that quinpirole inhibited the firing rate of all three types of striatal neurons in wild-type (WT) mice. However, in D2L knockout (KO) mice, quinpirole enhanced the excitability of ChIs, lost influence on spike firing of MSNs, and remained inhibitory effect on spike firing of FSIs. Additionally, we showed mIPSC frequency (but not mIPSC amplitude) was reduced in ChIs from D2L KO mice compared with WT mice, suggesting spontaneous GABA release is reduced at GABAergic terminals onto ChIs in D2L KO mice. Furthermore, we found D2L deficiency resulted in reduced dendritic spine density in ChIs, suggesting D2L activation plays a role in the formation/maintenance of dendritic spines of ChIs. These findings suggest new molecular and cellular mechanisms for causing ChIs abnormality seen in Parkinson’s disease or drug-induced dyskinesias.

Endocannabinoid-Mediated Control of Neural Circuit Excitability and Epileptic Seizures.

Research on endocannabinoid signaling has greatly advanced our understanding of how the excitability of neural circuits is controlled in health and disease. In general, endocannabinoid signaling at excitatory synapses suppresses excitability by inhibiting glutamate release, while that at inhibitory synapses promotes excitability by inhibiting GABA release, although there are some exceptions in genetically epileptic animal models. In the epileptic brain, the physiological distributions of endocannabinoid signaling molecules are disrupted during epileptogenesis, contributing to the occurrence of spontaneous seizures. However, it is still unknown how endocannabinoid signaling changes during seizures and how the redistribution of endocannabinoid signaling molecules proceeds during epileptogenesis. Recent development of cannabinoid sensors has enabled us to investigate endocannabinoid signaling in much greater spatial and temporal details than before. Application of cannabinoid sensors to epilepsy research has elucidated activity-dependent changes in endocannabinoid signaling during seizures. Furthermore, recent endocannabinoid research has paved the way for the clinical use of cannabidiol for the treatment of refractory epilepsy, such as Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex. Cannabidiol significantly reduces seizures and is considered to have comparable tolerability to conventional antiepileptic drugs. In this article, we introduce recent advances in research on the roles of endocannabinoid signaling in epileptic seizures and discuss future directions.

Presynaptic mechanisms underlying GABAB-receptor-mediated inhibition of spontaneous neurotransmitter release.

SUMMARYInhibition of neurotransmitter release by neurotransmitter substances constitutes a fundamental means of neuromodulation. In contrast to well-delineated mechanisms that underlie inhibition of evoked release via suppression of voltage-gated Ca2+ channels, processes that underlie neuromodulatory inhibition of spontaneous release remain unclear. Here, we interrogated inhibition of spontaneous glutamate and GABA release by presynaptic metabotropic GABAB receptors. Our findings show that this inhibition relies on Gβγ subunit action at the membrane, and it is largely independent of presynaptic Ca2+ signaling for both forms of release. In the case of spontaneous glutamate release, inhibition requires Gβγ interaction with the C terminus of the key fusion machinery component SNAP25, and it is modulated by synaptotagmin-1. Inhibition of spontaneous GABA release, on the other hand, is independent of these pathways and likely requires alternative Gβγ targets at the presynaptic terminal.

History-dependent dopamine release increases cAMP levels in most basal amygdala glutamatergic neurons to control learning.

Dopaminergic inputs to basal amygdala (BA) instruct learning of motivational salience. This learning depends on intracellular plasticity signals such as cyclic adenosine monophosphate (cAMP), which is regulated by activation of dopamine receptors. We examine the dynamics of dopamine release and downstream signaling during multiple salient events occurring within tens of seconds. We perform real-time tracking and manipulation of cAMP in BA neurons invitro and invivo. Optogenetically evoked release of dopamine drives proportional increases in cAMP in almost all BA glutamatergic neurons, suggesting widespread actions of dopamine across neurons preferring positive or negative valence. This cAMP response decreases across trials with short intertrial intervals owing to depression of dopamine release. No such depression is evident when photostimulating cAMP production directly. cAMP and protein kinase A responses to repeated appetitive or aversive stimuli also exhibit pronounced depression. Thus, history-dependent dynamics of dopamine and cAMP may regulate learning of temporally clustered, salient stimuli.

Hypothalamic melanin-concentrating hormone regulates hippocampus-dorsolateral septum activity.

Hypothalamic melanin-concentrating hormone (MCH) polypeptide contributes to regulating energy homeostasis, sleep, and memory, though the mechanistic bases of its effects are unknown. Here, in mice, we uncover the physiological mechanism underlying the functional role of MCH signaling in projections to the dorsolateral septum (dLS), a region involved in routing hippocampal firing rhythms and encoding spatial memory based on such rhythms. Firing activity within the dLS in response to dorsal CA3 (dCA3) excitation is limited by strong feed-forward inhibition (FFI). We find that MCH synchronizes dLS neuronal firing with its dCA3 inputs by enhancing GABA release, which subsequently reduces the FFI and augments dCA3 excitatory input strength, both via presynaptic mechanisms. At the functional level, our data reveal a role for MCH signaling in the dLS in facilitating spatial memory. These findings support a model in which peptidergic signaling within the dLS modulates dorsal hippocampal output and supports memory encoding.

Mild stress accumulation limits GABAergic synaptic plasticity in the lateral habenula.

Animals can cope with isolated stressful situations without enduring long‐term consequences. However, when exposure to stressors becomes recurrent, behavioural symptoms of anxiety and depression can emerge. Yet, the neuronal mechanisms governing responsivity to isolated stressor remain elusive. Here, we investigate synaptic adaptations following mild stress in the lateral habenula (LHb), a structure engaged in aversion encoding and dysfunctional in depression. We describe that neuronal depolarization in the LHb drives long‐term depression of inhibitory, but not excitatory, synaptic transmission (GABA LTD). This plasticity requires nitric oxide and presynaptic GABAB receptors, leading to a decrease in probability of GABA release. Mild stressors such as brief social isolation, or exposure to novel environment in the company of littermates, do not alter GABA LTD. In contrast, GABA LTD is absent after mice experience a novel environment in social isolation. Altogether, our results suggest that LHb GABAergic plasticity is sensitive to stress accumulation, which could represent a threshold mechanism for long‐term alterations of LHb function.

Low p-SYN1 (Ser-553) Expression Leads to Abnormal Neurotransmitter Release of GABA Induced by Up-Regulated Cdk5 after Microwave Exposure: Insights on Protection and Treatment of Microwave-Induced Cognitive Dysfunction.

With the wide application of microwave technology, concerns about its health impact have arisen. The signal transmission mode of the central nervous system and neurons make it particularly sensitive to electromagnetic exposure. It has been reported that abnormal release of amino acid neurotransmitters is mediated by alteration of p-SYN1 after microwave exposure, which results in cognitive dysfunction. As the phosphorylation of SYN1 is regulated by different kinases, in this study we explored the regulatory mechanisms of SYN1 fluctuations following microwave exposure and its subsequent effect on GABA release, aiming to provide clues on the mechanism of cognitive impairment caused by microwave exposure. In vivo studies with Timm and H&E staining were adopted and the results showed abnormality in synapse formation and neuronal structure, explaining the previously-described deficiency in cognitive ability caused by microwave exposure. The observed alterations in SYN1 level, combined with the results of earlier studies, indicate that SYN1 and its phosphorylation status (ser-553 and ser62/67) may play a role in the abnormal release of neurotransmitters. Thus, the role of Cdk5, the upstream kinase regulating the formation of p-SYN1 (ser-553), as well as that of MEK, the regulator of p-SYN1 (ser-62/67), were investigated both in vivo and in vitro. The results showed that Cdk5 was a negative regulator of p-SYN1 (ser-553) and that its up-regulation caused a decrease in GABA release by reducing p-SYN1 (ser-553). While further exploration still needed to elaborate the role of p-SYN1 (ser-62/67) for neurotransmitter release, MEK inhibition had was no impact on p-Erk or p-SYN1 (ser-62/67) after microwave exposure. In conclusion, the decrease of p-SYN1 (ser-553) may result in abnormalities in vesicular anchoring and GABA release, which is caused by increased Cdk5 regulated through Calpain-p25 pathway after 30 mW/cm2 microwave exposure. This study provided a potential new strategy for the prevention and treatment of microwave-induced cognitive dysfunction.