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The consumption of alcohol and caffeine affects the lives of billions of individuals worldwide. Although recent evidence indicates that caffeine impairs the reinforcing properties of alcohol, a characterization of its effects on alcohol-stimulated mesolimbic dopamine (DA) function was lacking. Acting as the pro-drug of salsolinol, alcohol excites DA neurons in the posterior ventral tegmental area (pVTA) and increases DA release in the nucleus accumbens shell (AcbSh). Here we show that caffeine, via antagonistic activity on A2A adenosine receptors (A2AR), prevents alcohol-dependent activation of mesolimbic DA function as assessed, in-vivo, by brain microdialysis of AcbSh DA and, in-vitro, by electrophysiological recordings of pVTA DA neuronal firing. Accordingly, while the A1R antagonist DPCPX fails to prevent the effects of alcohol on DA function, both caffeine and the A2AR antagonist SCH 58261 prevent alcohol-dependent pVTA generation of salsolinol and increase in AcbSh DA in-vivo, as well as alcohol-dependent excitation of pVTA DA neurons in-vitro. However, caffeine also prevents direct salsolinol- and morphine-stimulated DA function, suggesting that it can exert these inhibitory effects also independently from affecting alcohol-induced salsolinol formation or bioavailability. Finally, untargeted metabolomics of the pVTA showcases that caffeine antagonizes alcohol-mediated effects on molecules (e.g. phosphatidylcholines, fatty amides, carnitines) involved in lipid signaling and energy metabolism, which could represent an additional salsolinol-independent mechanism of caffeine in impairing alcohol-mediated stimulation of mesolimbic DA transmission. In conclusion, the outcomes of this study strengthen the potential of caffeine, as well as of A2AR antagonists, for future development of preventive/therapeutic strategies for alcohol use disorder.

Developmental myelination is a protracted process in the mammalian brain1. One theory for why oligodendrocytes mature so slowly posits that myelination may stabilize neuronal circuits and temper neuronal plasticity as animals age2-4. We tested this theory in the visual cortex, which has a well-defined critical period for experience-dependent neuronal plasticity5. During adolescence, visual experience modulated the rate of oligodendrocyte maturation in visual cortex. To determine whether oligodendrocyte maturation in turn regulates neuronal plasticity, we genetically blocked oligodendrocyte differentiation and myelination in adolescent mice. In adult mice lacking adolescent oligodendrogenesis, a brief period of monocular deprivation led to a significant decrease in visual cortex responses to the deprived eye, reminiscent of the plasticity normally restricted to adolescence. This enhanced functional plasticity was accompanied by a greater turnover of dendritic spines and coordinated reductions in spine size following deprivation. Furthermore, inhibitory synaptic transmission, which gates experience-dependent plasticity at the circuit level, was diminished in the absence of adolescent oligodendrogenesis. These results establish a critical role for oligodendrocytes in shaping the maturation and stabilization of cortical circuits and support the concept of developmental myelination acting as a functional brake on neuronal plasticity.

Adherens junction-associated protein 1 (AJAP1) has been implicated in brain diseases; however, a pathogenic mechanism has not been identified. AJAP1 is widely expressed in neurons and binds to γ-aminobutyric acid type B receptors (GBRs), which inhibit neurotransmitter release at most synapses in the brain. Here, we show that AJAP1 is selectively expressed in dendrites and trans-synaptically recruits GBRs to presynaptic sites of neurons expressing AJAP1. We have identified several monoallelic AJAP1 variants in individuals with epilepsy and/or neurodevelopmental disorders. Specifically, we show that the variant p.(W183C) lacks binding to GBRs, resulting in the inability to recruit them. Ultrastructural analysis revealed significantly decreased presynaptic GBR levels in Ajap1-/- and Ajap1W183C/+ mice. Consequently, these mice exhibited reduced GBR-mediated presynaptic inhibition at excitatory and inhibitory synapses, along with impaired synaptic plasticity. Our study reveals that AJAP1 enables the postsynaptic neuron to regulate the level of presynaptic GBR-mediated inhibition, supporting the clinical relevance of loss-of-function AJAP1 variants.

Parasympathetic dysfunction after chronic myocardial infarction (MI) is known to predispose ventricular tachyarrhythmias (ventricular tachycardia/ventricular fibrillation [VT/VF]). VT/VF after MI is more common in males than females. The mechanisms underlying the decreased vagal tone and the associated sex difference in the occurrence of VT/VF after MI remain elusive. In this study, using optogenetic approaches, we found that responses of glutamatergic vagal afferent neurons were impaired following chronic MI in male mice, leading to reduced reflex efferent parasympathetic function. Molecular analyses of vagal ganglia demonstrated reduced glutamate levels, accompanied by decreased mitochondrial function and impaired redox status in infarcted males versus sham animals. Interestingly, infarcted females demonstrated reduced vagal sensory impairment, associated with greater vagal ganglia glutamate levels and decreased vagal mitochondrial dysfunction and oxidative stress compared with infarcted males. Treatment with 17β-estradiol mitigated this pathological remodeling and improved vagal neurotransmission in infarcted male mice. These data suggest that a decrease in efferent vagal tone following MI results from reduced glutamatergic afferent vagal signaling that may be due to impaired redox homeostasis in the vagal ganglia, which subsequently leads to pathological remodeling in a sex-dependent manner. Importantly, estrogen prevents pathological remodeling and improves parasympathetic function following MI.

The brain bidirectionally communicates with the gut to control food intake and energy balance, which becomes dysregulated in obesity. For example, endocannabinoid (eCB) signaling in the small-intestinal (SI) epithelium is upregulated in diet-induced obese (DIO) mice and promotes overeating by a mechanism that includes inhibiting gut-brain satiation signaling. Upstream neural and molecular mechanism(s) involved in overproduction of orexigenic gut eCBs in DIO, however, are unknown. We tested the hypothesis that overactive parasympathetic signaling at the muscarinic acetylcholine receptors (mAChRs) in the SI increases biosynthesis of the eCB, 2-arachidonoyl-sn-glycerol (2-AG), which drives hyperphagia via local CB1Rs in DIO. Male mice were maintained on a high-fat/high-sucrose Western-style diet for 60 d, then administered several mAChR antagonists 30 min prior to tissue harvest or a food intake test. Levels of 2-AG and the activity of its metabolic enzymes in the SI were quantitated. DIO mice, when compared to those fed a low-fat/no-sucrose diet, displayed increased expression of cFos protein in the dorsal motor nucleus of the vagus, which suggests an increased activity of efferent cholinergic neurotransmission. These mice exhibited elevated levels of 2-AG biosynthesis in the SI, that was reduced to control levels by mAChR antagonists. Moreover, the peripherally restricted mAChR antagonist, methylhomatropine bromide, and the peripherally restricted CB1R antagonist, AM6545, reduced food intake in DIO mice for up to 24 h but had no effect in mice conditionally deficient in SI CB1Rs. These results suggest that hyperactivity at mAChRs in the periphery increases formation of 2-AG in the SI and activates local CB1Rs, which drives hyperphagia in DIO.

The ability of neurons to rapidly remodel their synaptic structure and strength in response to neuronal activity is highly conserved across species and crucial for complex brain functions. However, mechanisms required to elicit and coordinate the acute, activity-dependent structural changes across synapses are not well understood, as neurodevelopment and structural plasticity are tightly linked. Here, using an RNAi screen in Drosophila against genes affecting nervous system functions in humans, we uncouple cellular processes important for synaptic plasticity and synapse development. We find mutations associated with neurodegenerative and mental health disorders are 2-times more likely to affect activity-induced synaptic remodeling than synapse development. We report that while both synapse development and activity-induced synaptic remodeling at the fly NMJ require macroautophagy (hereafter referred to as autophagy), bifurcation in the autophagy pathway differentially impacts development and synaptic plasticity. We demonstrate that neuronal activity enhances autophagy activation but diminishes degradative autophagy, thereby driving the pathway towards autophagy-based secretion. Presynaptic knockdown of Snap29, Sec22, or Rab8, proteins implicated in the secretory autophagy pathway, is sufficient to abolish activity-induced synaptic remodeling. This study uncovers secretory autophagy as a transsynaptic signaling mechanism modulating synaptic plasticity.

Stable matching of neurotransmitters with their receptors is fundamental to synapse function and reliable communication in neural circuits. Presynaptic neurotransmitters regulate the stabilization of postsynaptic transmitter receptors. Whether postsynaptic receptors regulate stabilization of presynaptic transmitters has received less attention. Here, we show that blockade of endogenous postsynaptic acetylcholine receptors (AChR) at the neuromuscular junction destabilizes the cholinergic phenotype in motor neurons and stabilizes an earlier, developmentally transient glutamatergic phenotype. Further, expression of exogenous postsynaptic gamma-aminobutyric acid type A receptors (GABAA receptors) in muscle cells stabilizes an earlier, developmentally transient GABAergic motor neuron phenotype. Both AChR and GABAA receptors are linked to presynaptic neurons through transsynaptic bridges. Knockdown of specific components of these transsynaptic bridges prevents stabilization of the cholinergic or GABAergic phenotypes. Bidirectional communication can enforce a match between transmitter and receptor and ensure the fidelity of synaptic transmission. Our findings suggest a potential role of dysfunctional transmitter receptors in neurological disorders that involve the loss of the presynaptic transmitter.

Spontaneously occurring miniature excitatory postsynaptic currents (mEPSCs) are fundamental electrophysiological events produced by quantal vesicular transmitter release at synapses. Their analysis can provide important information regarding pre- and postsynaptic function. However, the small signal relative to recording noise requires expertise and considerable time for their identification. Furthermore, many mEPSCs smaller than ~8 pA are not well resolved (e.g., those produced at distant synapses or synapses with few receptor channels). Here, we describe an automated approach to detect mEPSCs using a machine learning-based tool. This method, which can be easily generalized to other one-dimensional signals, eliminates inter-observer bias, provides an estimate of its sensitivity and specificity and permits reliable detection of small (e.g., 5 pA) spontaneous unitary synaptic events.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impaired social interactions and verbal communication, accompanied by symptoms of restricted and repetitive patterns of behavior or interest. Over the past 30 years, the morbidity of ASD has increased in most areas of the world. Although the pathogenesis of ASD is not fully understood, it has been associated with over 1000 genes or genomic loci, indicating the importance and complexity of the genetic mechanisms involved. This review focuses on the synaptic pathology of ASD and particularly on genetic variants involved in synaptic structure and functions. These include SHANK, NLGN, NRXN, FMR1, and MECP2 as well as other potentially novel genes such as CHD8, CHD2, and SYNGAP1 that could be core elements in ASD pathogenesis. Here, we summarize several pathological pathways supporting the hypothesis that synaptic pathology caused by genetic mutations may be the pathogenic basis for ASD. [ABSTRACT FROM AUTHOR]

AMPA receptors (AMPARs) are the main drivers of excitatory glutamatergic transmission in the brain, central to synaptic plasticity, and are key drug targets. However, AMPARs are expressed in virtually every neuron in the central nervous system and are activated with complex temporal dynamics, making it difficult to determine their functional roles with sufficient precision. Here we describe a cell specific, light‐controllable competitive antagonist for the AMPA receptor called MP‐GluAblock that combines the temporal precision of a photo‐switchable ligand with the spatial and cellular specificity of a genetically‐encoded membrane‐anchor protein. This tool could pave the way for controlling endogenous AMPARs in neural circuits with cellular, spatial, and temporal specificity. [ABSTRACT FROM AUTHOR]

The discovery of adult‐born granule cells (aDGCs) in the dentate gyrus of the hippocampus has raised questions regarding how they develop, incorporate into the hippocampal circuitry, and contribute to learning and memory. Here, we used patch‐clamp electrophysiology to investigate the intrinsic and synaptic excitability of mouse aDGCs as they matured, enabled by using a tamoxifen‐induced genetic label to birth date the aDGCs at different animal ages. Importantly, we also undertook immunofluorescence studies of the expression of the immediate early gene Egr1 and compared these findings with the electrophysiology data in the same animals. We examined two groups of animals, with aDGC birthdating when the mice were 2 months and at 7–9 months of age. In both groups, cells 4 weeks old had lower thresholds for current‐evoked action potentials than older cells but fired fewer spikes during long current pulses and responded more poorly to synaptic activation. aDGCs born in both 2 and 7–9‐month‐old mice matured in their intrinsic excitability and synaptic properties from 4–12 weeks postgenesis, but this occurred more slowly for the older age animals. Interestingly, this pattern of intrinsic excitability changes did not correlate with the pattern of Egr1 expression. Instead, the development of Egr1 expression was correlated with the frequency of spontaneous excitatory postsynaptic currents. These results suggest that in order for aDGCs to fully participate in hippocampal circuitry, as indicated by Egr1 expression, they must have developed enough synaptic input, in spite of the greater input resistance and reduced firing threshold that characterizes young aDGCs. [ABSTRACT FROM AUTHOR]

The contribution of excitatory amino acids (AA) to ischemic brain injury has been widely described. In addition, we reported that a mixture of non-excitatory AA at plasmatic concentrations turns irreversible the depression of synaptic transmission caused by hypoxia. Here, we describe that the presence of seven non-excitatory AA (L-alanine, L-glutamine, glycine, L-histidine, L-serine, taurine, and L-threonine) during hypoxia provokes an irreversible neuronal membrane depolarization, after an initial phase of hyperpolarization. The collapse of the membrane potential correlates with a great increase in fiber volley amplitude. Nevertheless, we show that the presence of all seven AA is not necessary to cause the irreversible loss of fEPSP after hypoxia and that the minimal combination of AA able to provoke a solid, replicable effect is the mixture of L-alanine, glycine, L-glutamine, and L-serine. Additionally, L-glutamine seems necessary but insufficient to induce these harmful effects. We also prove that the deleterious effects of the AA mixtures on field potentials during hypoxia depend on both the identity and concentration of the individual AA in the mixture. Furthermore, we find that the accumulation of AA in the whole slice does not determine the outcome caused by the AA mixtures on the synaptic transmission during hypoxia. Finally, results obtained using pharmacological inhibitors and specific substrates of AA transporters suggest that system N and the alanine-serine-cysteine transporter 2 (ASCT2) participate in the non-excitatory AA-mediated deleterious effects during hypoxia. Thus, these AA transporters might represent therapeutical targets for the treatment of brain ischemia. [ABSTRACT FROM AUTHOR]

It is widely acknowledged that microglia actively regulate synaptic function in the brain. Remarkably, much of our understanding regarding the role of microglia in synaptic regulation is derived from studies in acute brain slices. However, it is still uncertain to what extent the preparation and maintenance of acute slices can influence microglial function and whether microglial changes may affect synaptic transmission. In this study, we examined the impact of acute slice resting time on hippocampal CA1 microglia, by assessing morphological and functional parameters at two distinct time intervals. We report that after 4 h from slicing microglia undergo morphological, functional, and transcriptional changes, including a decrease in the number of branches and in their movement speed. Furthermore, microglia acquire a reactive phenotype, characterized by increased amplitude of outward rectifying K+ currents, increased expression of the pro-inflammatory cytokine Tnfα and altered expression of the microglial receptors Cx3cr1 and P2y12r. We also examined time-dependent changes of excitatory synaptic transmission in CA1 pyramidal neurons from acute hippocampal slices, reporting time-dependent decrease in both amplitude and frequency of postsynaptic currents (sEPSCs), along with a decrease in spine density. Noticeably, sEPSCs amplitude decrease was absent in slices prepared from PLX5622 microglia-depleted mice, suggesting that this time-dependent effect on synaptic transmission is microglia-dependent. Our findings highlight possible causal relation between microglia phenotypic changes in the hours following slice preparation and concomitant synaptic changes, pointing to the mechanisms of acute synaptic modulation, whose understanding is crucial for unraveling microglia-neurons interplay in nature. Furthermore, they emphasize the potential issues associated with experimental time windows in ex vivo samples. [ABSTRACT FROM AUTHOR]

Feedback at the photoreceptor synapse is the first neuronal circuit computation in vision, which influences downstream activity patterns within the visual system. Yet, the identity of the feedback signal and the mechanism of synaptic transmission are still not well understood. Here, we combined perturbations of cell-type-specific genes of mouse horizontal cells with two-photon imaging of the result of light-induced feedback in cones and showed that the electrogenic bicarbonate transporter Slc4a5, but not the electroneutral bicarbonate transporter Slc4a3, both expressed specifically in horizontal cells, is necessary for horizontal cell-to-cone feedback. Pharmacological blockage of bicarbonate transporters and buffering pH also abolished the feedback but blocking sodium-proton exchangers and GABA receptors did not. Our work suggests an unconventional mechanism of feedback at the first visual synapse: changes in horizontal cell voltage modulate bicarbonate transport to the cell, via Slc4a5, which leads to the modulation of feedback to cones. [Display omitted] • Feedback from horizontal cells to cones was measured by imaging calcium in cones • Slc4a5 is an electrogenic Na+-HCO 3 − cotransporter specific to horizontal cells • Knocking out or down Slc4a5 abolished horizontal cell-to-cone feedback • Blocking HCO 3 − transporters and buffering pH also abolished feedback Molecular mechanisms of horizontal cell-to-cone feedback in the retina have been under debate. Morikawa et al. show that Slc4a5, an electrogenic sodium-bicarbonate cotransporter specific to horizontal cells, is crucial for feedback. They suggest that Slc4a5, through its voltage-dependent transport of bicarbonate, regulates pH in the synaptic cleft that mediates feedback. [ABSTRACT FROM AUTHOR]

The suprachiasmatic nucleus is the circadian pacemaker of the mammalian brain. Suprachiasmatic nucleus neurons display synchronization of their firing frequency on a circadian timescale, which is required for the pacemaker function of the suprachiasmatic nucleus. However, the mechanisms by which suprachiasmatic nucleus neurons remain synchronized in vivo are poorly understood, although synaptic communication is considered indispensable. Suprachiasmatic nucleus neurons contain the neurotransmitter GABA and express GABA receptors. This has inspired the hypothesis that GABA signalling may play a central role in network synchronization, although this remains untested in vivo. Here, using local genetic deletion, we show that disruption of GABA synaptic transmission within the suprachiasmatic nucleus of adult mice results in the eventual deterioration of physiological and behavioural rhythmicity in vivo and concomitant cellular desynchrony in vitro. These findings suggest that intercellular GABA signalling is essential for behavioural rhythmicity and cellular synchrony of the suprachiasmatic nucleus neural network. [ABSTRACT FROM AUTHOR]

Alcohol is the most consumed and abused psychoactive drug globally, but the molecular mechanisms driving alcohol action and its associated behaviors in the brain remain enigmatic. Here, we have discovered a transmembrane protein TMEM132B that is a GABA A receptor (GABA A R) auxiliary subunit. Functionally, TMEM132B promotes GABA A R expression at the cell surface, slows receptor deactivation, and enhances the allosteric effects of alcohol on the receptor. In TMEM132B knockout (KO) mice or TMEM132B I499A knockin (KI) mice in which the TMEM132B-GABA A R interaction is specifically abolished, GABAergic transmission is decreased and alcohol-induced potentiation of GABA A R-mediated currents is diminished in hippocampal neurons. Behaviorally, the anxiolytic and sedative/hypnotic effects of alcohol are markedly reduced, and compulsive, binge-like alcohol consumption is significantly increased. Taken together, these data reveal a GABA A R auxiliary subunit, identify the TMEM132B-GABA A R complex as a major alcohol target in the brain, and provide mechanistic insights into alcohol-related behaviors. [Display omitted] • Single-pass transmembrane protein TMEM132B is a GABA A R auxiliary subunit • TMEM132B promotes GABA A R expression at the cell surface and slows receptor deactivation • TMEM132B enhances the allosteric effects of alcohol on various GABA A Rs • Genetic inactivation of TMEM132B in mice alters alcohol-related behaviors Identification of TMEM132B as a GABA A R auxiliary subunit that modulates alcohol action in the brain at both the molecular and behavioral levels. [ABSTRACT FROM AUTHOR]

Norepinephrine (NE) modulates synaptic transmission and long-term plasticity through distinct subtype adrenergic receptor (AR)-mediated-intracellular signaling cascades. However, the role of NE modulates glutamatergic long-term potentiation (LTP) in the hypothalamic paraventricular nucleus (PVN) magnocellular neuroendocrine cells (MNCs) is unclear. We here investigate the effect of NE on high frequency stimulation (HFS)-induced glutamatergic LTP in rat hypothalamic PVN MNCs in vitro, by whole-cell patch-clamp recording, biocytin staining and pharmacological methods. Delivery of HFS induced glutamatergic LTP with a decrease in N2/N1 ratio in the PVN MNCs, which was enhanced by application of NE (100 nM). HFS-induced LTP was abolished by the blockade of N-methyl-D-aspartate receptors (NMDAR) with D-APV, but it was rescued by the application of NE. NE failed to rescue HFS-induced LTP of MNCs in the presence of a selective β1-AR antagonist, CGP 20712. However, application of β1-AR agonist, dobutamine HCl rescued HFS-induced LTP of MNCs in the absence of NMDAR activity. In the absence of NMDAR activity, NE failed to rescue HFS-induced MNC LTP when protein kinase A (PKA) was inhibited by extracellular applying KT5720 or intracellular administration of PKI. These results indicate that NE activates β1-AR and triggers HFS to induce a novel glutamatergic LTP of hypothalamic PVN NMCs via the postsynaptic PKA signaling pathway in vitro in rats. [ABSTRACT FROM AUTHOR]

Emerged evidence indicated that stimulating hippocampal neurogenesis is a potential strategy for restoring cognition in AD. Mitogen‐activated protein kinases (MAPKs) play an essential role in neurogenesis. Meanwhile, the enzymatic power of the phosphatases is much greater than that of kinases. Dual‐specificity phosphatase 16 (DUSP16), known to as a phosphatase negatively regulate MAPKs, may be implicated in neural differentiation. Nevertheless, the effect of DUSP16 on cognitive disorders by stimulating neural progenitor cell (NPC) differentiation in AD mice remains unclear. Our study demonstrates an association between DUSP16 SNPs and clinical progression in individuals with mild cognitive impairment (MCI). Besides, increased DUSP16 expression was detected in both 3xTg and SAMP8 mouse models of AD, accompanied by NPC neural differentiation impairments. By silencing DUSP16, the induction of neural differentiation, synaptic transmission, and cognitive benefits were observed in both AD mice. Furthermore, DUSP16 was involved in the process of NPC differentiation through regulating c‐Jun N‐terminal kinase (JNK) phosphorylation and SOX2 expression. Moreover, ETS transcription factor (ELK1) was involved in the DUSP16 transcription, which resulted in the upregulation of DUSP16 at the state of AD. Our data uncovers a potential regulatory role for DUSP16 in adult hippocampal neurogenesis (AHN) and provides a possibility to find a novel strategy for AD intervention. [ABSTRACT FROM AUTHOR]

Motor ability decline remains a major threat to the quality of life of the elderly. Although the later stages of aging co-exist with degenerative pathologies, the long process of aging is more complicated than a simple and gradual degeneration. To combat senescence and the associated late-stage degeneration of the neuromuscular system, it is imperative to examine changes that occur during the long process of aging. Prior to late-stage degeneration, age-induced changes in the neuromuscular system trigger homeostatic plasticity. This unique phenomenon may be important for the maintenance of the neuromuscular system during the early stages of aging. In this review, we will focus on age-induced changes in neurotransmission at the neuromuscular junction, providing the potential mechanisms responsible for these changes. The goal is to highlight these key elements and their role in regulating neurotransmission, facilitating future research efforts to combat late-stage degeneration in the neuromuscular system by preserving the functional and structural integrity of these elements prior to the late stage of aging. [ABSTRACT FROM AUTHOR]

The trigeminal sensory system consists of the trigeminal nerve, the trigeminal ganglion, and the trigeminal sensory nuclei (the mesencephalic nucleus, the principal nucleus, the spinal trigeminal nucleus, and several smaller nuclei). Various sensory signals carried by the trigeminal nerve from the orofacial area travel into the trigeminal sensory system, where they are processed into integrated sensory information that is relayed to higher sensory brain areas. Thus, knowledge of the trigeminal sensory system is essential for comprehending orofacial pain. This review elucidates the individual nuclei that comprise the trigeminal sensory system and their synaptic transmission. Additionally, it discusses four types of orofacial pain and their relationship to the system. Consequently, this review aims to enhance the understanding of the mechanisms underlying orofacial pain. [ABSTRACT FROM AUTHOR]

A whole‐cell patch‐clamp study was carried out to investigate membrane and synaptic properties of cholinergic interneurons in the striatum of aristaless‐related homeobox gene (ARX) mutant mice. Brain slices were prepared from mice knocked in two types of ARX, P355L (PL) and 333ins (GCG)7 (GCG). The input resistance of cholinergic interneurons in PL or GCG mice was significantly smaller than that in wild type (WT), whereas resting membrane potential, threshold of action potentials, spontaneous firing rate, sag ratio or afterhyperpolarization of the mutant mice were not significantly different from those of WT mice. In GCG mice, NMDA/AMPA ratio of excitatory postsynaptic currents (EPSCs) evoked in cholinergic interneurons was significantly smaller than that in WT and PL mice, whereas the ratio between PL and WT mice was not significantly different. Although inhibitory effects induced by dopamine D2‐like receptor activation on the inhibitory postsynaptic currents (IPSCs) were not significantly different between WT and PL or GCG mice, increase in the paired pulse ratio of IPSCs by dopamine D2‐like receptor activation was abolished in PL and GCG mice. The present results have found abnormalities of neuronal activities as well as its modulation in the basal ganglia in ARX mutant mice, clarifying basic mechanisms underlying related disorders. [ABSTRACT FROM AUTHOR]

α‐Amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) ionotropic glutamate receptors (AMPARs) mediate rapid excitatory synaptic transmission in the mammalian brain, primarily driven by the neurotransmitter glutamate. The modulation of AMPAR activity, particularly calcium‐permeable AMPARs (CP‐AMPARs), is crucially influenced by various auxiliary subunits. These subunits are integral membrane proteins that bind to the receptor's core and modify its functional properties, including ion channel kinetics and receptor trafficking. This review comprehensively catalogs all known AMPAR auxiliary proteins, providing vital insights into the biochemical mechanisms governing synaptic modulation and the specific impact of CP‐AMPARs compared to their calcium‐impermeable AMPA receptor (CI‐AMPARs). Understanding the complex interplay between AMPARs and their auxiliary subunits in different brain regions is essential for elucidating their roles in cognitive functions such as learning and memory. Importantly, alterations in these auxiliary proteins' expression, function or interactions have been implicated in various neurological disorders. Aberrant signaling through CP‐AMPARs, in particular, is associated with severe synaptic dysfunctions across neurodevelopmental, neurodegenerative and psychiatric conditions. Targeting the distinct properties of AMPAR‐auxiliary subunit complexes, especially those involving CP‐AMPARs, could disclose new therapeutic strategies, potentially allowing for more precise interventions in treating complex neuronal disorders. [ABSTRACT FROM AUTHOR]

Communication between neurons and glia significantly influences the development maturation, plasticity, and disease progressions of the nervous system. As a new signaling modality, extracellular vesicles display a diverse role for robust functional regulation of neurons through their protein and nucleic acid cargoes. This review highlights recent breakthroughs in the research of signaling mechanisms between glia and neurons mediated by extracellular vesicles that are important for neural development, axonal maintenance, synaptic functions, and disease progression in the mammalian nervous system. We will discuss the biological roles of extracellular vesicles released from neurons, astroglia, microglia, and oligodendroglia in the nervous system and their implications in neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

Ubiquitin ligases are important regulators of nervous system development, function and disease. To date, numerous ubiquitin ligases have been discovered that regulate presynaptic biology. Here, we discuss recent findings on presynaptic ubiquitin ligases that include members from the three major ubiquitin ligase classes: RING, RBR and HECT. Several themes emerge based on findings across a range of model systems. A cadre of ubiquitin ligases is required presynaptically to orchestrate development and transmission at synapses. Multiple ubiquitin ligases deploy both enzymatic and non‐enzymatic mechanisms, and act as hubs for signalling networks at the synapse. Both excitatory and inhibitory presynaptic terminals are influenced by ligase activity. Finally, there are several neurodevelopmental disorders and neurodegenerative diseases associated with presynaptic ubiquitin ligases. These findings highlight the growing prominence and biomedical relevance of the presynaptic ubiquitin ligase network. [ABSTRACT FROM AUTHOR]

The recent increase in the use of nicotine products by teenagers has revealed an urgent need to better understand the impact of nicotine on the adolescent brain. Here, we sought to examine the actions of extracellular ATP as a neurotransmitter and to investigate whether ATP and nicotinic signaling interact during adolescence. With the GRABATP (G-protein-coupled receptor activation-based ATP sensor), we first demonstrated that nicotine induces extracellular ATP release in the medial habenula, a brain region involved in nicotine aversion and withdrawal. Using patch-clamp electrophysiology, we then demonstrated that activation of the ATP receptors P2X or P2Y1 increases the neuronal firing of cholinergic neurons. Surprisingly, contrasting interactive effects were observed with nicotine exposure. For the P2X receptor, activation had no observable effect on acute nicotine-mediated activity, but during abstinence after 10 d of nicotine exposure, coexposure to nicotine and the P2X agonist potentiated neuronal activity in female, but not male, neurons. For P2Y1 signaling, a potentiated effect of the agonist and nicotine was observed with acute exposure, but not following extended nicotine exposure. These data reveal a complex interactive effect between nicotinic and ATP signaling in the adolescent brain and provide mechanistic insights into extracellular ATP signaling with sex-specific alterations of neuronal responses based on prior drug exposure.SIGNIFICANCE STATEMENT In these studies, it was discovered that nicotine induces extracellular ATP release in the medial habenula and subsequent activation of the ATP purinergic receptors increases habenular cholinergic neuronal firing in the adolescent brain. Interestingly, following extended nicotine exposure, nicotine was found to alter the interplay between purinergic and nicotinic signaling in a sex-specific manner. Together, these studies provide a novel understanding for the role of extracellular ATP in mediating habenular activity and reveal how nicotine exposure during adolescence alters these signaling mechanisms, which has important implications given the high incidence of e-cigarette/vape use by youth.

The vestibular hair cell receptors of anamniotes, designated Type II, are presynaptic to bouton endings of vestibular nerve distal neurites. An additional flask-shaped hair cell receptor, Type I, is present in amniotes, and communicates with a chalice-shaped afferent neuritic ending that surrounds the entire hair cell except its apical neck. Since the full repertoire of afferent fiber dynamics and sensitivities observed throughout the vertebrate phyla can be accomplished through Type II hair cell-bouton synapses, the functional contribution(s) of Type I hair cells and their calyces to vestibular performance remains a topic of great interest. The goal of the present study was to investigate electrical coupling between the Type I hair cell and its enveloping calyx in the mouse semicircular canal crista ampullaris. Since there are no gap junctions between these two cells, evidence for electrical communication would necessarily involve other mechanisms. Simultaneous recordings from the two cells of the synaptic pair were used initially to verify the presence of orthodromic quantal synaptic transmission from the hair cell to the calyx, and then to demonstrate bi-directional communication due to the slow accumulation of potassium ions in the synaptic cleft. As a result of this potassium ion accretion, the equilibrium potentials of hair cell conductances facing the synaptic cleft become depolarized to an extent that is adequate for calcium influx into the hair cell, and the calyx inner face becomes depolarized to a level that is near the threshold for spike initiation. Following this, paired recordings were again employed to characterize fast bi-directional electrical coupling between the two cells. In this form of signaling, cleft-facing conductances in both the hair cell and calyx increase, which strengthens their coupling. Because this mechanism relies on the cleft resistance, we refer to it as resistive coupling. We conclude that the same three forms of hair cell-calyceal transmission previously demonstrated in the turtle are present in the mammalian periphery, providing a biophysical basis for the exceptional temporal fidelity of the vestibular system. [ABSTRACT FROM AUTHOR]

FKBP51, also known as FK506‐binding protein 51, is a molecular chaperone and scaffolding protein with significant roles in regulating hormone signaling and responding to stress. Genetic variants in FKBP5, which encodes FKBP51, have been implicated in a growing number of neuropsychiatric disorders, which has spurred efforts to target FKBP51 therapeutically. However, the molecular mechanisms and sub‐anatomical regions influenced by FKBP51 in these disorders are not fully understood. In this study, we aimed to examine the impact of Fkbp5 ablation using circadian phenotyping and molecular analyses. Our findings revealed that the lack of FKBP51 did not significantly alter circadian rhythms, as detected by wheel‐running activity, but did offer protection against stress‐mediated disruptions in rhythmicity in a sex‐dependent manner. Protein changes in Fkbp5 KO mice, as measured by histology and proteomics, revealed alterations in a brain region‐ and sex‐dependent manner. Notably, regardless of sex, aged Fkbp5 KOs showed elevated MYCBP2, FBXO45, and SPRYD3 levels, which are associated with neuronal‐cell adhesion and synaptic integrity. Additionally, pathways such as serotonin receptor signaling and S100 family signaling were differentially regulated in Fkbp5 KO mice. Weighted protein correlation network analysis identified protein networks linked with synaptic transmission and neuroinflammation. The information generated by this work can be used to better understand the molecular changes in the brain during aging and in the absence of Fkbp5, which has implications for the continued development of FKBP51‐focused therapeutics for stress‐related disorders. [ABSTRACT FROM AUTHOR]

Since their discovery nearly 30 years ago, fibroblast growth factor homologous factors (FHFs) are now known to control the functionality of excitable tissues through a range of mechanisms. Nervous and cardiac system dysfunctions are caused by loss‐ or gain‐of‐function mutations in FHF genes. The best understood 'canonical' targets for FHF action are voltage‐gated sodium channels, and recent studies have expanded the repertoire of ways that FHFs modulate sodium channel gating. Additional 'non‐canonical' functions of FHFs in excitable and non‐excitable cells, including cancer cells, have been reported over the past dozen years. This review summarizes and evaluates reported canonical and non‐canonical FHF functions. [ABSTRACT FROM AUTHOR]

The subiculum is a key region of the brain involved in the initiation of pathological activity in temporal lobe epilepsy, and local GABAergic inhibition is essential to prevent subicular‐originated epileptiform discharges. Subicular pyramidal cells may be easily distinguished into two classes based on their different firing patterns. Here, we have compared the strength of the GABAa receptor‐mediated inhibitory postsynaptic currents received by regular‐ vs. burst‐firing subicular neurons and their dynamic modulation by the activation of μ opioid receptors. We have taken advantage of the sequential re‐patching of the same cell to initially classify pyramidal neurons according to their firing patters, and then to measure GABAergic events triggered by the optogenetic stimulation of parvalbumin‐ and somatostatin‐expressing interneurons. Activation of parvalbumin‐expressing cells generated larger responses in postsynaptic burst‐firing neurons whereas the opposite was observed for currents evoked by the stimulation of somatostatin‐expressing interneurons. In all cases, events depended critically on ω‐agatoxin IVA‐ but not on ω‐conotoxin GVIA‐sensitive calcium channels. Optogenetic GABAergic input originating from both parvalbumin‐ and somatostatin‐expressing cells was reduced in amplitude following the exposure to a μ opioid receptor agonist. The kinetics of this pharmacological sensitivity was different in regular‐ vs. burst‐firing neurons, but only when responses were evoked by the activation of parvalbumin‐expressing neurons, whereas no differences were observed when somatostatin‐expressing cells were stimulated. In conclusion, our results show that a high degree of complexity regulates the organizing principles of subicular GABAergic inhibition, with the interaction of pre‐ and postsynaptic diversity at multiple levels. Key points: Optogenetic stimulation of parvalbumin‐ and somatostatin‐expressing interneurons (PVs and SOMs) triggers inhibitory postsynaptic currents (IPSCs) in both regular‐ and burst‐firing (RFs and BFs) subicular pyramidal cells.The amplitude of optogenetically evoked IPSCs from PVs (PV‐opto IPSCs) is larger in BFs whereas IPSCs generated by the light activation of SOMs (SOM‐opto IPSCs) are larger in RFs.Both PV‐ and SOM‐opto IPSCs critically depend on ω‐agatoxin IVA‐sensitive P/Q type voltage‐gated calcium channels, whereas no major effects are observed following exposure to ω‐conotoxin GVIA, suggesting no significant involvement of N‐type channels.The amplitude of both PV‐ and SOM‐opto IPSCs is reduced by the probable pharmacological activation of presynaptic μ opioid receptors, with a faster kinetics of the effect observed in PV‐opto IPSCs from RFs vs. BFs, but not in SOM‐opto IPSCs.These results help us understand the complex interactions between different layers of diversity regulating GABAergic input onto subicular microcircuits. [ABSTRACT FROM AUTHOR]

Circadian fluctuations in physiological setpoints are determined by the suprachiasmatic nucleus (SCN) which exerts control over many target structures within and beyond the hypothalamus via projections. The SCN, or central pacemaker, orchestrates synchrony between the external environment and the internal circadian mechanism. The resulting cycles in hormone levels and autonomic nervous system (ANS) activity provide precise messages to specific organs, adjusting, for example, their sensitivity to approaching hormones or metabolites. The SCN responds to both photic (light) and non-photic input. Circadian patterns are found in both heart rate and blood pressure, which are linked to daily variations in activity and autonomic nervous system activity. Variations in blood pressure are of great interest as several cardiovascular diseases such as stroke, arrhythmias, and hypertension are linked to circadian rhythm dysregulation. The disruption of normal day-night cycles, such as in shift work, social jetlag, or eating outside of normal hours leads to desynchronization of the central and peripheral clocks. This desynchronization leads to disorganization of the cellular processes that are normally driven by the interactions of the SCN and photic input. Here, we review autonomic system function and dysfunction due to regulation and interaction between different cardiorespiratory brain centers and the SCN, as well as social, lifestyle, and external factors that may impact the circadian control of blood pressure. [ABSTRACT FROM AUTHOR]

Artemisinin (ART) and its derivatives, collectively referred to as artemisinins (ARTs), have been approved for the treatment of malaria for decades. ARTs are converted into dihydroartemisinin (DHA), the only active form, which is reductive in vivo. In this review, we provide a brief overview of the neuroprotective potential of ARTs and the underlying mechanisms on several of the most common neurodegenerative diseases, particularly considering their potential application in those associated with cognitive and motor impairments including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). ARTs act as autophagy balancers to alleviate AD and PD. They inhibit neuroinflammatory responses by regulating phosphorylation of signal transduction proteins, such as AKT, PI3K, ERK, NF-κB, p38 MAPK, IκBα. In addition, ARTs regulate GABAergic signaling in a dose-dependent manner. Although they competitively inhibit the binding of gephyrin to GABAergic receptors, low doses of ARTs enhance GABAergic signaling. ARTs can also inhibit ferroptosis, activate the Akt/Bcl-2, AMPK, or ERK/CREB pathways to reduce oxidative stress, and maintain mitochondrial homeostasis, protecting neurons from oxidative stress injury. More importantly, ARTs structurally combine with and suppress β-Amyloid (A β) -induced neurotoxicity, reduce P-tau, and maintain O-GlcNAcylation/Phosphorylation balance, leading to relieved pathological changes in neurodegenerative diseases. Collectively, these natural properties endow ARTs with unique potential for application in neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

Neurons rely on mitochondrial energy metabolism for essential functions like neurogenesis, neurotransmission, and synaptic plasticity. Mitochondrial dysfunctions are associated with neurodevelopmental disorders including Fragile X syndrome (FXS), the most common cause of inherited intellectual disability, which also presents with motor skill deficits. However, the precise role of mitochondria in the pathophysiology of FXS remains largely unknown. Notably, previous studies have linked the serotonergic system and mitochondrial activity to FXS. Our study investigates the potential therapeutic role of serotonin receptor 1A (5-HT1A) in FXS. Using the Drosophila model of FXS, we demonstrated that treatment with eltoprazine, a 5-HT1A agonist, can ameliorate synaptic transmission, correct mitochondrial deficits, and ultimately improve motor behavior. While these findings suggest that the 5-HT1A-mitochondrial axis may be a promising therapeutic target, further investigation is needed in the context of FXS. [ABSTRACT FROM AUTHOR]

The dispanins are a family of transmembrane proteins with diverse and often unclear physiological functions. Many dispanins are expressed in the central nervous system, where they are involved in the development and maturation of synapses, the regulation of neurotransmitter release, and interactions with ion channels, including AMPA receptors. The roles of dispanins expressed in the peripheral nervous system are not as clear. Recently, a family of neurotoxins isolated from Australian stinging trees were shown to target dispanins in the periphery to modulate the function of voltage-gated sodium channels. This positions dispanins as an inherently druggable class of transmembrane proteins that may be targeted for the treatment of dispanin-associated neurological disease. The dispanins are a family of 15 transmembrane proteins that have diverse and often unclear physiological functions. Many dispanins, including synapse differentiation induced gene 1 (SynDIG1), proline-rich transmembrane protein 1 (PRRT1)/SynDIG4, and PRRT2, are expressed in the central nervous system (CNS), where they are involved in the development of synapses, regulation of neurotransmitter release, and interactions with ion channels, including AMPA receptors (AMPARs). Others, including transmembrane protein 233 (TMEM233) and trafficking regulator of GLUT4-1 (TRARG1), are expressed in the peripheral nervous system (PNS); however, the function of these dispanins is less clear. Recently, a family of neurotoxins isolated from the giant Australian stinging tree was shown to target TMEM233 to modulate the function of voltage-gated sodium (Na V) channels, suggesting that the dispanins are inherently druggable. Here, we review current knowledge about the structure and function of the dispanins, in particular TMEM233 and its two most closely related homologs PRRT2 and TRARG1, which may be drug targets involved in neurological disease. [ABSTRACT FROM AUTHOR]

Three decades ago, the first endocannabinoid, anandamide (AEA), was identified, and its analgesic effect was recognized in humans and preclinical models. However, clinical trial failures pointed out the complexity of the AEA-induced analgesia. The first synapses in the superficial laminae of the spinal cord dorsal horn represent an important modulatory site in nociceptive transmission and subsequent pain perception. The glutamatergic synaptic transmission at these synapses is strongly modulated by two primary AEA-activated receptors, cannabinoid receptor 1 (CB1) and transient receptor potential vanilloid 1 (TRPV1), both highly expressed on the presynaptic side formed by the endings of primary nociceptive neurons. Activation of these receptors can have predominantly inhibitory (CB1) and excitatory (TRPV1) effects that are further modulated under pathological conditions. In addition, dual AEA-mediated signaling and action may occur in primary sensory neurons and dorsal horn synapses. AEA application causes balanced inhibition and excitation of primary afferent synaptic input on superficial dorsal horn neurons in normal conditions, whereas peripheral inflammation promotes AEA-mediated inhibition. This review focuses mainly on the modulation of synaptic transmission at the spinal cord level and signaling in primary nociceptive neurons by AEA via CB1 and TRPV1 receptors. Furthermore, the spinal analgesic effect in preclinical studies and clinical aspects of AEA-mediated analgesia are considered. [ABSTRACT FROM AUTHOR]

N-Methyl-D-aspartate receptors (NMDARs), encoded by GRIN genes, are ionotropic glutamate receptors playing a critical role in synaptic transmission, plasticity, and synapse development. Genome sequence analyses have identified variants in GRIN genes in patients with neurodevelopmental disorders, but the underlying disease mechanisms are not well understood. Here, we have created and evaluated a transgenic mouse line carrying a missense variant Grin2bL825V, corresponding to a de novo GRIN2B variant encoding GluN2B(L825V) found in a patient with intellectual disability (ID) and autismspectrum disorder (ASD). We used HEK293T cells expressing recombinant receptors and primary hippocampal neurons prepared from heterozygous Grin2bL825V/+ (L825V/+) and wild-type (WT) Grin2b+/+ (+/+) male and female mice to assess the functional impact of the variant. Whole-cell NMDAR currents were reduced in neurons from L825V/+ compared with +/+ mice. The peak amplitude of NMDAR-mediated evoked excitatory postsynaptic currents (NMDAR-eEPSCs) was unchanged, but NMDAR-eEPSCs in L825V/+ neurons had faster deactivation compared with +/+ neurons and were less sensitive to a GluN2B-selective antagonist ifenprodil. Together, these results suggest a decreased functional contribution of GluN2B subunits to synaptic NMDAR currents in hippocampal neurons from L825V/+ mice. The analysis of the GluN2B(L825V) subunit surface expression and synaptic localization revealed no differences compared with WT GluN2B. Behavioral testing of mice of both sexes demonstrated hypoactivity, anxiety, and impaired sensorimotor gating in the L825V/+ strain, particularly affecting males, as well as cognitive symptoms. The heterozygous L825V/+ mouse offers a clinically relevant model of GRIN2B-related ID/ASD, and our results suggest synaptic-level functional changes that may contribute to neurodevelopmental pathology. [ABSTRACT FROM AUTHOR]

The release of neurotransmitters (NTs) at central synapses is dependent on a cascade of protein interactions, specific to the presynaptic compartment. Among those dedicated molecules, the cytosolic complexins play an incompletely defined role as synaptic transmission regulators. Complexins are multidomain proteins that bind soluble N-ethylmaleimide sensitive factor attachment protein receptor complexes, conferring both inhibitory and stimulatory functions. Using systematic mutagenesis and comparing reconstituted in vitro membrane fusion assays with electrophysiology in cultured neurons from mice of either sex, we deciphered the function of the N-terminus of complexin (Cpx) II. The N-terminus (amino acid 1-27) starts with a region enriched in hydrophobic amino acids (1-12), which binds lipids. Mutants maintaining this hydrophobic character retained the stimulatory function of Cpx, whereas exchanges introducing charged residues perturbed both spontaneous and evoked exocytosis. Mutants in the more distal region of the N-terminal domain (amino acid 11-18) showed a spectrum of effects. On the one hand, mutation of residue A12 increased spontaneous release without affecting evoked release. On the other hand, replacing D15 with amino acids of different shapes or hydrophobic properties (but not charge) not only increased spontaneous release but also impaired evoked release. Most surprising, this substitution reduced the size of the readily releasable pool, a novel function for Cpx at mammalian synapses. Thus, the exact amino acid composition of the Cpx N-terminus fine-tunes the degree of spontaneous and evoked NT release. [ABSTRACT FROM AUTHOR]

Chronic intermittent hypoxia (CIH) in rodents mimics the hypoxia‐induced elevation of blood pressure seen in individuals experiencing episodic breathing. The brainstem nucleus tractus solitarii (nTS) is the first site of visceral sensory afferent integration, and thus is critical for cardiorespiratory homeostasis and its adaptation during a variety of stressors. In addition, the paraventricular nucleus of the hypothalamus (PVN), in part through its nTS projections that contain oxytocin (OT) and/or corticotropin‐releasing hormone (CRH), contributes to cardiorespiratory regulation. Within the nTS, these PVN‐derived neuropeptides alter nTS activity and the cardiorespiratory response to hypoxia. Nevertheless, their contribution to nTS activity after CIH is not fully understood. We hypothesized that OT and CRH would increase nTS activity to a greater extent following CIH, and co‐activation of OT+CRH receptors would further magnify nTS activity. Our data show that compared to their normoxic controls, 10 days' CIH exaggerated nTS discharge, excitatory synaptic currents and Ca2+ influx in response to CRH, which were further enhanced by the addition of OT. CIH increased the tonic functional contribution of CRH receptors, which occurred with elevation of mRNA and protein. Together, our data demonstrate that intermittent hypoxia exaggerates the expression and function of neuropeptides on nTS activity. Key points: Episodic breathing and chronic intermittent hypoxia (CIH) are associated with autonomic dysregulation, including elevated sympathetic nervous system activity. Altered nucleus tractus solitarii (nTS) activity contributes to this response.Neurons originating in the paraventricular nucleus (PVN), including those containing oxytocin (OT) and corticotropin‐releasing hormone (CRH), project to the nTS, and modulate the cardiorespiratory system. Their role in CIH is unknown.In this study, we focused on OT and CRH individually and together on nTS activity from rats exposed to either CIH or normoxia control.We show that after CIH, CRH alone and with OT increased to a greater extent overall nTS discharge, neuronal calcium influx, synaptic transmission to second‐order nTS neurons, and OT and CRH receptor expression.These results provide insights into the underlying circuits and mechanisms contributing to autonomic dysfunction during periods of episodic breathing. [ABSTRACT FROM AUTHOR]

The spatial distribution of proteins and their arrangement within the cellular ultrastructure regulates the opening of a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in response to glutamate release at the synapse. Fluorescence microscopy imaging revealed that the postsynaptic density (PSD) and scaffolding proteins in the presynaptic active zone (AZ) align across the synapse to form a trans-synaptic "nanocolumn," but the relation to synaptic vesicle release sites is uncertain. Here, we employ focused-ion beam (FIB) milling and cryoelectron tomography to image synapses under near-native conditions. Improved image contrast, enabled by FIB milling, allows simultaneous visualization of supramolecular nanoclusters within the AZ and PSD and synaptic vesicles. Surprisingly, membrane-proximal synaptic vesicles, which fuse to release glutamate, are not preferentially aligned with AZ or PSD nanoclusters. These synaptic vesicles are linked to the membrane by peripheral protein densities, often consistent in size and shape with Munc13, as well as globular densities bridging the synaptic vesicle and plasma membrane, consistent with prefusion complexes of SNAREs, synaptotagmins, and complexin. Monte Carlo simulations of synaptic transmission events using biorealistic models guided by our tomograms predict that clustering AMPARs within PSD nanoclusters increases the variability of the postsynaptic response but not its average amplitude. Together, our data support a model in which synaptic strength is tuned at the level of single vesicles by the spatial relationship between scaffolding nanoclusters and single synaptic vesicle fusion sites. [ABSTRACT FROM AUTHOR]

The goal of this report is to explore how K2P channels modulate axonal excitability by using the crayfish ventral superficial flexor preparation. This preparation allows for simultaneous recording of motor nerve extracellular action potentials (eAP) and intracellular excitatory junctional potential (EJP) from a muscle fiber. Previous pharmacological studies have demonstrated the presence of K2P‐like channels in crayfish. Fluoxetine (50 µM) was used to block K2P channels in this study. The blocker caused a gradual decline, and eventually complete block, of motor axon action potentials. At an intermediate stage of the block, when the peak‐to‐peak amplitude of eAP decreased to ∼60%–80% of the control value, the amplitude of the initial positive component of eAP declined at a faster rate than that of the negative peak representing sodium influx. Furthermore, the second positive peak following this sodium influx, which corresponds to the after‐hyperpolarizing phase of intracellularly recorded action potentials (iAP), became larger during the intermediate stage of eAP block. Finally, EJP recorded simultaneously with eAP showed no change in amplitude, but did show a significant increase in synaptic delay. These changes in eAP shape and EJP delay are interpreted as the consequence of depolarized resting membrane potential after K2P channel block. In addition to providing insights to possible functions of K2P channels in unmyelinated axons, results presented here also serve as an example of how changes in eAP shape contain information that can be used to infer alterations in intracellular events. This type of eAP‐iAP cross‐inference is valuable for gaining mechanistic insights here and may also be applicable to other model systems. [ABSTRACT FROM AUTHOR]

The aim of this study was to identify key proteins of synaptic transmission in the cochlear nucleus (CN) that are involved in normal hearing, acoustic stimulation, and tinnitus. A gene list was compiled from the GeneCards database using the keywords "synaptic transmission" AND "tinnitus" AND "cochlear nucleus" (Tin). For comparison, two gene lists with the keywords "auditory perception" (AP) AND "acoustic stimulation" (AcouStim) were built. The STRING protein–protein interaction (PPI) network and the Cytoscape data analyzer were used to identify the top two high-degree proteins (HDPs) and their high-score interaction proteins (HSIPs), together referred to as key proteins. The top1 key proteins of the Tin-process were BDNF, NTRK1, NTRK3, and NTF3; the top2 key proteins are FOS, JUN, CREB1, EGR1, MAPK1, and MAPK3. Highly significant GO terms in CN in tinnitus were "RNA polymerase II transcription factor complex", "late endosome", cellular response to cadmium ion", "cellular response to reactive oxygen species", and "nerve growth factor signaling pathway", indicating changes in vesicle and cell homeostasis. In contrast to the spiral ganglion, where important changes in tinnitus are characterized by processes at the level of cells, important biological changes in the CN take place at the level of synapses and transcription. [ABSTRACT FROM AUTHOR]

Long-term potentiation (LTP) was used to gauge the impact of conventional and FLASH dose rates on synaptic transmission. Data collected from the hippocampus and medial prefrontal cortex confirmed significant inhibition of LTP after 10 fractions of 3 Gy (30 Gy total) conventional radiotherapy. Remarkably, 10x3Gy FLASH radiotherapy and unirradiated controls were identical and exhibited normal LTP.

Here, we introduce the full functional reconstitution of genetically validated core protein machinery (SNAREs, Munc13, Munc18, Synaptotagmin, and Complexin) for synaptic vesicle priming and release in a geometry that enables detailed characterization of the fate of docked vesicles both before and after release is triggered with Ca2+. Using this setup, we identify new roles for diacylglycerol (DAG) in regulating vesicle priming and Ca2+-triggered release involving the SNARE assembly chaperone Munc13. We find that low concentrations of DAG profoundly accelerate the rate of Ca2+-dependent release, and high concentrations reduce clamping and permit extensive spontaneous release. As expected, DAG also increases the number of docked, release-ready vesicles. Dynamic single-molecule imaging of Complexin binding to release-ready vesicles directly establishes that DAG accelerates the rate of SNAREpin assembly mediated by chaperones, Munc13 and Munc18. The selective effects of physiologically validated mutations confirmed that the Munc18-Syntaxin-VAMP2 template complex is a functional intermediate in the production of primed, release-ready vesicles, which requires the coordinated action of Munc13 and Munc18.

The ability to appropriately update the value of a given action is a critical component of flexible decision making. Several psychiatric disorders, including schizophrenia, are associated with impairments in flexible decision making that can be evaluated using the probabilistic reversal learning (PRL) task. The PRL task has been reverse-translated for use in rodents. Disrupting glutamate neurotransmission during early postnatal neurodevelopment in rodents has induced behavioral, cognitive, and neuropathophysiological abnormalities relevant to schizophrenia. Here, we tested the hypothesis that using the NMDA receptor antagonist phencyclidine (PCP) to disrupt postnatal glutamatergic transmission in rats would lead to impaired decision making in the PRL. Consistent with this hypothesis, compared to controls the postnatal PCP-treated rats completed fewer reversals and exhibited disruptions in reward and punishment sensitivity (i.e., win-stay and lose-shift responding, respectively). Moreover, computational analysis of behavior revealed that postnatal PCP-treatment resulted in a pronounced impairment in the learning rate throughout PRL testing. Finally, a deep neural network (DNN) trained on the rodent behavior could accurately predict the treatment group of subjects. These data demonstrate that disrupting early postnatal glutamatergic neurotransmission impairs flexible decision making and provides evidence that DNNs can be trained on behavioral datasets to accurately predict the treatment group of new subjects, highlighting the potential for DNNs to aid in the diagnosis of schizophrenia.

AMPA receptors (AMPARs) are the major mediators of fast excitatory neurotransmission in the retina as in other parts of the brain. In most neurons, the synaptic targeting, pharmacology, and function of AMPARs are influenced by auxiliary subunits including the transmembrane AMPA receptor regulatory proteins (TARPs). However, it is unclear which TARP subunits are present at retinal synapses and how they influence receptor localization and function. Here, we show that TARPɣ2 (stargazin) is associated with AMPARs in the synaptic layers of the mouse, rabbit, macaque, and human retina. In most species, TARPɣ2 expression was high where starburst amacrine cells (SACs) ramify and transcriptomic analyses suggest correspondingly high gene expression in mouse and human SACs. Synaptic expression of GluA2, GluA3, and GluA4 was significantly reduced in a mouse mutant lacking TARPɣ2 expression (stargazer mouse; stg), whereas GluA1 levels were unaffected. AMPAR-mediated light-evoked EPSCs in ON-SACs from stg mice were ∼30% smaller compared with heterozygous littermates. There was also loss of a transient ON pathway-driven GABAergic input to ON-SACs in stg mutants. Direction-selective ganglion cells in the stg mouse showed normal directional tuning, but their surround inhibition and thus spatial tuning was reduced. Our results indicate that TARPɣ2 is required for normal synaptic expression of GluA2, GluA3, and GluA4 in the inner retina. The presence of residual AMPAR expression in the stargazer mutant suggests that other TARP subunits may compensate in the absence of TARPɣ2.

Midbrain dopamine (DA) neurons are key regulators of basal ganglia functions. The axonal domain of these neurons is highly complex, with a large subset of non-synaptic release sites and a smaller subset of synaptic terminals from which in addition to DA, glutamate or GABA are also released. The molecular mechanisms regulating the connectivity of DA neurons and their neurochemical identity are unknown. An emerging literature suggests that neuroligins, trans-synaptic cell adhesion molecules, regulate both DA neuron connectivity and neurotransmission. However, the contribution of their major interaction partners, neurexins (Nrxns), is unexplored. Here, we tested the hypothesis that Nrxns regulate DA neuron neurotransmission. Mice with conditional deletion of all Nrxns in DA neurons (DAT::NrxnsKO) exhibited normal basic motor functions. However, they showed an impaired locomotor response to the psychostimulant amphetamine. In line with an alteration in DA neurotransmission, decreased levels of the membrane DA transporter (DAT) and increased levels of the vesicular monoamine transporter (VMAT2) were detected in the striatum of DAT::NrxnsKO mice, along with reduced activity-dependent DA release. Strikingly, electrophysiological recordings revealed an increase of GABA co-release from DA neuron axons in the striatum of these mice. Together, these findings suggest that Nrxns act as regulators of the functional connectivity of DA neurons.

Early life stress alters gut microbiota and increases the risk of neuropsychiatric disorders, including social deficits and anxiety, in the host. However, the role of gut commensal bacteria in early life stress-induced neurobehavioral abnormalities remains unclear. Using the maternally separated (MS) mice, our research has unveiled a novel aspect of this complex relationship. We discovered that the reduced levels of amino acid transporters in the intestine of MS mice led to low glutamine (Gln) levels in the blood and synaptic dysfunction in the medial prefrontal cortex (mPFC). Abnormally low blood Gln levels limit the brain’s availability of Gln, which is required for presynaptic glutamate (Glu) and γ-aminobutyric acid (GABA) replenishment. Furthermore, MS resulted in gut microbiota dysbiosis characterized by a reduction in the relative abundance of Lactobacillus reuteri (L. reuteri). Notably, supplementation with L. reuteri ameliorates neurobehavioral abnormalities in MS mice by increasing intestinal amino acid transport and restoring synaptic transmission in the mPFC. In conclusion, our findings on the role of L. reuteri in regulating intestinal amino acid transport and buffering early life stress-induced behavioral abnormalities provide a novel insight into the microbiota-gut-brain signaling basis for emotional behaviors.

ABSTRACTVoltage-gated calcium channels (VGCCs) are the major conduits for calcium ions (Ca2+) within excitable cells. Recent studies have highlighted the non-ionotropic functionality of VGCCs, revealing their capacity to activate intracellular pathways independently of ion flow. This non-ionotropic signaling mode plays a pivotal role in excitation-coupling processes, including gene transcription through excitation-transcription (ET), synaptic transmission via excitation-secretion (ES), and cardiac contraction through excitation-contraction (EC). However, it is noteworthy that these excitation-coupling processes require extracellular calcium (Ca2+) and Ca2+ occupancy of the channel ion pore. Analogous to the “non-canonical” characterization of the non-ionotropic signaling exhibited by the N-methyl-D-aspartate receptor (NMDA), which requires extracellular Ca2+ without the influx of ions, VGCC activation requires depolarization-triggered conformational change(s) concomitant with Ca2+ binding to the open channel. Here, we discuss the contributions of VGCCs to ES, ET, and EC coupling as Ca2+ binding macromolecules that transduces external stimuli to intracellular input prior to elevating intracellular Ca2+. We emphasize the recognition of calcium ion occupancy within the open ion-pore and its contribution to the excitation coupling processes that precede the influx of calcium. The non-ionotropic activation of VGCCs, triggered by the upstroke of an action potential, provides a conceptual framework to elucidate the mechanistic aspects underlying the microseconds nature of synaptic transmission, cardiac contractility, and the rapid induction of first-wave genes.

It is widely acknowledged that microglia actively regulate synaptic function in the brain. Remarkably, much of our understanding regarding the role of microglia in synaptic regulation is derived from studies in acute brain slices. However, it is still uncertain to what extent the preparation and maintenance of acute slices can influence microglial function and whether microglial changes may affect synaptic transmission. In this study, we examined the impact of acute slice resting time on hippocampal CA1 microglia, by assessing morphological and functional parameters at two distinct time intervals. We report that after 4 h from slicing microglia undergo morphological, functional, and transcriptional changes, including a decrease in the number of branches and in their movement speed. Furthermore, microglia acquire a reactive phenotype, characterized by increased amplitude of outward rectifying K+ currents, increased expression of the pro-inflammatory cytokine Tnfα and altered expression of the microglial receptors Cx3cr1 and P2y12r. We also examined time-dependent changes of excitatory synaptic transmission in CA1 pyramidal neurons from acute hippocampal slices, reporting time-dependent decrease in both amplitude and frequency of postsynaptic currents (sEPSCs), along with a decrease in spine density. Noticeably, sEPSCs amplitude decrease was absent in slices prepared from PLX5622 microglia-depleted mice, suggesting that this time-dependent effect on synaptic transmission is microglia-dependent. Our findings highlight possible causal relation between microglia phenotypic changes in the hours following slice preparation and concomitant synaptic changes, pointing to the mechanisms of acute synaptic modulation, whose understanding is crucial for unraveling microglia-neurons interplay in nature. Furthermore, they emphasize the potential issues associated with experimental time windows in ex vivo samples.

Decelerating motor decline is important for promoting healthy aging in the elderly population. Acorus tatarinowii Schott is a traditional Chinese medicine that contains β-asarone as a pharmacologically active constituent. We found that β-asarone can decelerate motor decline in various age groups of Caenorhabditis elegans, while concurrently prolonging their lifespan and modulating synaptic transmission. To understand the mechanisms of its efficacy in motor improvement, we investigated and discovered that mitochondrial fragmentation, a marker for aging, is delayed after β-asarone treatment. Moreover, their efficacy is blocked by dysfunctional mitochondria. Corresponding to their role in regulating mitochondrial homeostasis, we found that SKN-1/Nrf2 and GST-4 are critical in the β-asarone treatment, and they appear to be activated via the insulin/IGF-1 signaling pathway. Well-developed intestinal microvilli are required for this process. Our study demonstrates the efficacy and mechanism of β-asarone treatment in age-related motor decline, contributing to the discovery of drugs for achieving healthy aging.