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Social novelty impairment is a hallmark feature of autism spectrum disorder associated with synaptic dysfunction. While G-protein coupled receptor 158 (GPR158) has been shown to be essential for synaptic neurotransmission, its role in modulating social novelty remains unknown. Here, we investigated the impact of GPR158 on social behavior in mice and observed that both constitutive and cell/tissue-specific knockout ofGpr158in pyramidal neurons or the medial prefrontal cortex (mPFC) result in impaired novelty preference, but not sociability. Notably, we found a significant decline in excitatory synaptic transmission and glutamate vesicles in the mPFC synapses of globalGpr158knockouts. Mechanistically, we identified that constitutive loss ofGpr158led to suppressed Vglut1 distribution, possibly resulting from altered expression of vesicular V-ATPases and SNAREs byGpr158ablation in pyramidal neurons. Our findings suggest that GPR158 in pyramidal neurons specifically modulates social novelty and may be a potential therapeutic target for treating social disorders.Graphic AbstractHighlightsKnockout ofGpr158causes social novelty deficit in mice.Knockout ofGpr158in pyramidal neurons leads to disrupted synaptic transmission and an E-I imbalance in the mPFC.Disturbed E-I homeostasis in the mPFC is likely due to reduced density of glutamate vesicles caused byGpr158knockout.

Background Microdeletion of the 16p11.2 region of the human chromosome is a prevalent genetic factor for autism spectrum disorder (ASD) and other neurodevelopmental disorders, but its pathogenic mechanism remains unclear, and effective treatments for 16p11.2 microdeletion syndrome are lacking. Emerging evidence suggests that the gut microbiota and its metabolites are inextricably linked to host behavior through the gut-brain axis, and are therefore implicated in ASD development. However, the functional roles of microbial metabolites in the context of 16p11.2 microdeletion are yet to be elucidated. This study aims to investigate the therapeutic potential of indole-3-propionic acid (IPA), a gut microbiota metabolite, in addressing behavioral and pathological deficits associated with 16p11.2 microdeletion, as well as the underlying molecular mechanisms. Results Mice with the 16p11.2 microdeletion (16p11.2+/−) showed dysbiosis of the gut microbiota and a significant decrease in IPA levels in feces and blood circulation. Further, these mice exhibited significant social and cognitive impairments, and abnormal activation of hippocampal dentate gyrus neurons, which was accompanied by an imbalance of inhibitory synaptic transmission in this region. However, oral supplementation of IPA significantly mitigated these alterations, thereby ameliorating the social and cognitive deficits of the mice. Remarkably, IPA administration significantly increased the phosphorylation level of ERK1, a protein encoded by the Mapk3 gene in the 16p11.2 region, without affecting the transcription and translation of the Mapk3 gene. Conclusions Our study reveal that 16p11.2+/− leads to a decline in gut metabolite IPA levels, and that supplementation with IPA can reverse the associated histological and electrophysiological changes and behavioral defects in 16p11.2+/− mice. These findings provide new insights into the critical role of gut microbial metabolites in ASD pathogenesis and presents a promising treatment treatment strategy for social and cognitive deficit disorders, such as 16p11.2 microdeletion syndrome.

During ongoing presynaptic action potential (AP) firing, transmitter release is limited by the availability of release-ready synaptic vesicles (SVs). The rate of SV recruitment (SVR) to release sites is strongly upregulated at high AP frequencies to balance SV consumption. We show that Munc13-1—an essential SV priming protein—regulates SVR via a Ca2+-phospholipid-dependent mechanism. Using knockin mouse lines with point mutations in the Ca2+-phospholipid-binding C2B domain of Munc13-1, we demonstrate that abolishing Ca2+-phospholipid binding increases synaptic depression, slows recovery of synaptic strength after SV pool depletion, and reduces temporal fidelity of synaptic transmission, while increased Ca2+-phospholipid binding has the opposite effects. Thus, Ca2+-phospholipid binding to the Munc13-1-C2B domain accelerates SVR, reduces short-term synaptic depression, and increases the endurance and temporal fidelity of neurotransmission, demonstrating that Munc13-1 is a core vesicle priming hub that adjusts SV re-supply to demand.

To examine the preventive effect of heat preconditioning (HPC) on intraoperatively acquired pressure ulcers (IAPU) in surgical patients and explore the mechanisms of HPC on pressure injury (PI) in rat skin. We generated a skin PI model using hairless rats and treated these rats with HPC. Skin injury size was measured and the expression of heat shock proteins (HSPs) in the skin were examined by real-time RT PCR, Western blotting, and immunohistochemical staining. For human studies, 118 surgical patients were randomly divided into HPC and control groups. We measured sacral skin temperature, sacral pressure and compared the PI prevalence rate. HPC treatment significantly reduced both area(p =0.007, p =0.007, p =0.012) and incidence (p=0.025, p =0.019, p =0.012) of PI in rats on the second, third and fourth days. HSP27 expression was increased in HPC group. Immunohistochemical staining showed that HSP27 was distributed in all types of dermal cells with increase in basal cells. In human studies, HPC treatment increased sacral temperature (p. The incidence of IAPUs was significantly decreased by 75% in HPC group. HPC can reduce the incidence of PI in both experimental animals and humans. Beneficial effects of HPC were possibly mediated by upregulation of HSP27.

Summary During ongoing presynaptic action potential (AP) firing, transmitter release is limited by the availability of release-ready synaptic vesicles (SVs). The rate of SV recruitment (SVR) to release sites is strongly upregulated at high AP frequencies to balance SV consumption. We show that Munc13-1—an essential SV priming protein—regulates SVR via a Ca2+-phospholipid-dependent mechanism. Using knockin mouse lines with point mutations in the Ca2+-phospholipid-binding C2B domain of Munc13-1, we demonstrate that abolishing Ca2+-phospholipid binding increases synaptic depression, slows recovery of synaptic strength after SV pool depletion, and reduces temporal fidelity of synaptic transmission, while increased Ca2+-phospholipid binding has the opposite effects. Thus, Ca2+-phospholipid binding to the Munc13-1-C2B domain accelerates SVR, reduces short-term synaptic depression, and increases the endurance and temporal fidelity of neurotransmission, demonstrating that Munc13-1 is a core vesicle priming hub that adjusts SV re-supply to demand., Graphical abstract, Highlights • The Munc13-1 C2B domain controls synaptic vesicle replenishment rates • Blocking Ca2+-phospholipid-C2B signaling attenuates vesicle replenishment • Enhancing Ca2+-phospholipid-C2B signaling accelerates vesicle replenishment • This process determines short-term plasticity and fidelity of synaptic transmission, Using novel knockin mouse models, Lipstein et al. show that Ca2+-phospholipid binding activates the presynaptic protein Munc13-1 to fine-tune the rate of synaptic vesicle replenishment according to synaptic activity. This process determines short-term synaptic plasticity and the temporal fidelity of synaptic transmission in the auditory brainstem and the hippocampus.

The synaptic vesicle (SV) protein synaptotagmin-1 (Syt1) is the Ca2+ sensor for fast synchronous release. Biochemical and structural data suggest that Syt1 interacts with phospholipids and SNARE complex, but the manner in which these interactions translate into SV fusion remains poorly understood. Using flash-and-freeze electron microscopy, which triggers action potentials with light and coordinately arrests synaptic structures with rapid freezing, we found that synchronous-release-impairing mutations in the Syt1 C2B domain (K325, 327; R398, 399) also disrupt SV-active-zone plasma-membrane attachment. Single action potential induction rescued membrane attachment in these mutants within less than 10 ms through activation of the Syt1 Ca2+-binding site. The rapid SV membrane translocation temporarily correlates with resynchronization of release and paired pulse facilitation. On the basis of these findings, we redefine the role of Syt1 as part of the Ca2+-dependent vesicle translocation machinery and propose that Syt1 enables fast neurotransmitter release by means of its dynamic membrane attachment activities.

Neurotransmitter release requires the formation of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes by SNARE proteins syntaxin-1 (Stx1), synaptosomal-associated protein 25 (SNAP-25), and synaptobrevin-2 (Syb2). In mammalian systems, loss of SNAP-25 or Syb2 severely impairs neurotransmitter release; however, complete loss of function studies for Stx1 have been elusive due to the functional redundancy between Stx1 isoforms Stx1A and Stx1B and the embryonic lethality of Stx1A/1B double knock-out (DKO) mice. Here, we studied the roles of Stx1 in neuronal maintenance and neurotransmitter release in mice with constitutive or conditional deletion of Stx1B on an Stx1A-null background. Both constitutive and postnatal loss of Stx1 severely compromised neuronal viability in vivo and in vitro, indicating an obligatory role of Stx1 for maintenance of developing and mature neurons. Loss of Munc18-1, a high-affinity binding partner of Stx1, also showed severely impaired neuronal viability, but with a slower time course compared with Stx1A/1B DKO neurons, and exogenous Stx1A or Stx1B expression significantly delayed Munc18-1-dependent lethality. In addition, loss of Stx1 completely abolished fusion-competent vesicles and severely impaired vesicle docking, demonstrating its essential roles in neurotransmission. Putative partial SNARE complex assembly with the SNARE motif mutant Stx1A(AV) (A240V, V244A) was not sufficient to rescue neurotransmission despite full recovery of vesicle docking and neuronal survival. Together, these data suggest that Stx1 has independent functions in neuronal maintenance and neurotransmitter release and complete SNARE complex formation is required for vesicle fusion and priming, whereas partial SNARE complex formation is sufficient for vesicle docking and neuronal maintenance. SIGNIFICANCE STATEMENT Syntaxin-1 (Stx1) is a component of the synaptic vesicle soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex and is essential for neurotransmission. We present the first detailed loss-of-function characterization of the two Stx1 isoforms in central mammalian neurons. We show that Stx1 is fundamental for maintenance of developing and mature neurons and also for vesicle docking and neurotransmission. We also demonstrate that neuronal maintenance and neurotransmitter release are regulated by Stx1 through independent functions. Furthermore, we show that SNARE complex formation is required for vesicle fusion, whereas partial SNARE complex formation is sufficient for vesicle docking and neuronal maintenance. Therefore, our work provides insights into differential functions of Stx1 in neuronal maintenance and neurotransmission, with the latter explored further into its functions in vesicle docking and fusion.

Complexins (Cplxs) are small synaptic proteins that cooperate with SNARE-complexes in the control of synaptic vesicle (SV) fusion. Studies involving genetic mutation, knock-down, or knock-out indicated two key functions of Cplx that are not mutually exclusive but cannot easily be reconciled, one in facilitating SV fusion, and one in “clamping” SVs to prevent premature fusion. Most studies on the role of Cplxs in mammalian synapse function have relied on cultured neurons, heterologous expression systems, or membrane fusion assaysin vitro, whereas little is known about the function of Cplxs in native synapses. We therefore studied consequences of genetic ablation of Cplx1 in the mouse calyx of Held synapse, and discovered a developmentally exacerbating phenotype of reduced spontaneous and evoked transmission but excessive asynchronous release after stimulation, compatible with combined facilitating and clamping functions of Cplx1. Because action potential waveforms, Ca2+influx, readily releasable SV pool size, and quantal size were unaltered, the reduced synaptic strength in the absence of Cplx1 is most likely a consequence of a decreased release probability, which is caused, in part, by less tight coupling between Ca2+channels and docked SV. We found further that the excessive asynchronous release in Cplx1-deficient calyces triggered aberrant action potentials in their target neurons, and slowed-down the recovery of EPSCs after depleting stimuli. The augmented asynchronous release had a delayed onset and lasted hundreds of milliseconds, indicating that it predominantly represents fusion of newly recruited SVs, which remain unstable and prone to premature fusion in the absence of Cplx1.

Fundamental response properties of neurons centrally underly the computational capabilities of both individual nerve cells and neural networks. Most studies on neuronal input-output relations have focused on continuous-time inputs such as constant or noisy sinusoidal currents. Yet, most neurons communicate via exchanging action potentials (spikes) at discrete times. Here, we systematically analyze the stationary spiking response to regular spiking inputs and reveal that it is generically non-monotonic. Our theoretical analysis shows that the underlying mechanism relies solely on a combination of the discrete nature of the communication by spikes, the capability of locking output to input spikes and limited resources required for spike processing. Numerical simulations of mathematically idealized and biophysically detailed models, as well as neurophysiological experiments confirm and illustrate our theoretical predictions., Author Summary Brain function relies on robust communication between a huge number of nerve cells (neurons) that exchange short-lasting electrical pulses (called action potentials or spikes) at certain times. How nerve cells process their spiking inputs to generate spiking outputs thus is key not only to individual neurons’ computational capabilities but also to the collective dynamics of neuronal networks. Here we analyze the response properties of neurons to regular spike sequence inputs. We find that neurons typically respond in a non-monotonic way. Output frequency mostly increases with input frequency as expected but sometimes output frequency necessarily decreases upon increasing the input frequency. Our theoretical analysis predicts that spiking neurons commonly exhibit such non-monotonic response properties. Simulations of simple mathematical and complex computational models as well as neurophysiological experiments confirm our theoretical predictions.

Calyx and endbulb synapses of the mammalian auditory brainstem are specialized in transmitting spike activity fast, sustained and temporally precise. To accomplish this task, they make use of unusually large presynaptic elements which form axosomatic contacts with their postsynaptic target neurons. The large size of the calyceal terminals represents a major experimental advantage and has enabled electrophysiologists to study the functional properties of Ca2+ channels in presynaptic CNS terminals in great detail, with high time resolution and unprecedented precision. Calyx and endbulb terminals express several thousands of Ca2+ channels with rapid kinetics which ensure fast and efficient gating of Ca2+ influx during brief action potentials. When repetitively activated, presynaptic Ca2+ influx is modulated in a frequency-dependent manner and this Ca2+ current modulation contributes significantly to short-term plasticity at these synapses. During short high-frequency bursts, Ca2+ influx is facilitated whereas tetanic activity or low-frequency firing leads to an accumulation of Ca2+ channel inactivation. When the calyx synapses mature, the coupling between docked transmitter vesicles and Ca2+ channels becomes tighter to compensate for the shortening of the presynaptic action potential duration. Many of the G protein-dependent pathways of Ca2+ channel regulation that are potent in immature synapses are weakened during postnatal development.

Most neurons in the nervous system communicate by sending and receiving stereotyped electrical pulses called action potentials or spikes. The computational capabilities of neural circuits centrally rely on the input-output relations of single neurons. This relation is commonly characterized by its output spike rate in response to a temporally continuous constant input current, sometimes in the presence of additional current fluctuations [1]. If the spikes each neuron receives are irregular in time and individually only weakly affect the neuron's membrane potential, this continuous-input picture serves as an appropriate approximation [2] to the actual spike sequence input. As a consequence, a neuron's response curve in terms of its output spike rate, increasing monotonically as a function of input current, is considered one of its most important standard characteristics. Yet, a broad range of neural systems exhibit more regular, patterned spike sequences. Some experimental and numerical studies [3-5] suggest that certain neurons receiving correlated spiking inputs may exhibit non-monotonic input-output relations. Here we systematically analyze the stationary spiking response of neurons to regular spiking inputs and reveal that it is generically non-monotonic. Our theoretical analysis shows that the underlying mechanism relies solely on a combination of the discrete nature of the communication by spikes and limited resources required for spike processing. Numerical simulations of mathematically idealized and biophysically detailed models, as well as neurophysiological experiments confirm our theoretical predictions (Figure ​(Figure1).1). Non-monotonic response to regular spiking inputs thus is a generic feature common across spiking neurons. Figure 1 Non-monotonic response to regular spiking inputs as observed in neurons from the medial nucleus of the trapezoid body (MNTB) of rats. Shown is the measured output rate in dependence of the input rate of the neuron. Dashed lines indicate theoretical predictions ...

Complexins are small synaptic proteins which cooperate with the SNARE-complex during synaptic transmission. Different roles of complexins in the regulation of vesicle exocytosis have been proposed. Based on the results of genetic mutation or knock down/out studies, it is generally agreed that complexins are involved in vesicle priming and exocytosis during fast synchronous release and in clamping vesicles to prevent asynchronous release. However, depending on cell type, organism and experimental approach used, complexins appear to either facilitate or inhibit vesicle fusion. Here, we study the function of complexin I at the calyx of Held synapse. By taking advantage of the large size of the calyx terminal, allowing direct patch-clamp recordings, we investigate the consequences of the loss of function of complexin I. We demonstrate a developmentally aggravating phenotype of reduced EPSC amplitudes and enhanced asynchronous release. We provide evidence for a role of CPX I in recruiting Ca2+ channels to docked vesicles which may determine their release probability. The enhanced asynchronous release in complexin-deficient mice slowed-down the recovery of synchronous EPSCs after stimulus trains suggesting both, synchronous and asynchronous release events, were fed by a common pool of vesicles.