Contact-dependent aggregation of functional Ca 2+ channels, synaptic vesicles and postsynaptic receptors in active zones of a neuromuscular junction

Abstract To examine whether Ca 2+ channels aggregate in a contact-dependent manner, we characterized the distribution of synaptic vesicles and postsynaptic receptors, and compared it to the location of Ca 2+ entry sites, in a Xenopus laevis nerve-muscle coculture preparation using a localized Ca 2+ detection method. The majority (75%) of Ca 2+ entry sites at spontaneously formed nerve±muscle contacts were associated with enhanced immuno¯uorescence to the synaptic vesicle protein, SV2. In contrast, only 11% of recorded sites without Ca 2+ transients exhibited signi®cant SV2 immuno¯uorescence. When comparing the spatial distribution of synaptic markers with that of Ca 2+ entry sites, we found that the majority of Ca 2+ entry sites (61%) were associated with both enhanced SV2 immuno¯uorescence and R-BTX¯uorescence, thereby identifying putative neurotransmitter release sites where Ca 2+ channels, synaptic vesicles and postsynaptic receptors are colocalized. Using polystyrene beads coated with a heparin binding protein known to mediate in vitro postsynaptic receptor clustering, we show that the location of Ca 2+ domains was associated with enhanced SV2 immuno¯uorescence at neurite-to-bead contacts. We conclude that the localization of functional Ca 2+ channels to putative active zones follows a contact-dependent signalling mechanism similar to that known to mediate vesicle aggregation and AChR clustering

Modulation of γ-Secretase Reduces β-Amyloid Deposition in a Transgenic Mouse Model of Alzheimer's Disease

SummaryAlzheimer's disease (AD) is characterized pathologically by the abundance of senile plaques and neurofibrillary tangles in the brain. We synthesized over 1200 novel gamma-secretase modulator (GSM) compounds that reduced Aβ42 levels without inhibiting epsilon-site cleavage of APP and Notch, the generation of the APP and Notch intracellular domains, respectively. These compounds also reduced Aβ40 levels while concomitantly elevating levels of Aβ38 and Aβ37. Immobilization of a potent GSM onto an agarose matrix quantitatively recovered Pen-2 and to a lesser degree PS-1 NTFs from cellular extracts. Moreover, oral administration (once daily) of another potent GSM to Tg 2576 transgenic AD mice displayed dose-responsive lowering of plasma and brain Aβ42; chronic daily administration led to significant reductions in both diffuse and neuritic plaques. These effects were observed in the absence of Notch-related changes (e.g., intestinal proliferation of goblet cells), which are commonly associated with repeated exposure to functional gamma-secretase inhibitors (GSIs)

A Glial Variant of the Vesicular Monoamine Transporter Is Required To Store Histamine in the Drosophila Visual System

Unlike other monoamine neurotransmitters, the mechanism by which the brain's histamine content is regulated remains unclear. In mammals, vesicular monoamine transporters (VMATs) are expressed exclusively in neurons and mediate the storage of histamine and other monoamines. We have studied the visual system of Drosophila melanogaster in which histamine is the primary neurotransmitter released from photoreceptor cells. We report here that a novel mRNA splice variant of Drosophila VMAT (DVMAT-B) is expressed not in neurons but rather in a small subset of glia in the lamina of the fly's optic lobe. Histamine contents are reduced by mutation of dVMAT, but can be partially restored by specifically expressing DVMAT-B in glia. Our results suggest a novel role for a monoamine transporter in glia that may be relevant to histamine homeostasis in other systems

Modelling human choices: MADeM and decision‑making

Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)

26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017

This work was produced as part of the activities of FAPESP Research,\ud Disseminations and Innovation Center for Neuromathematics (grant\ud 2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud supported by a CNPq fellowship (grant 306251/2014-0)

Feed-forward recruitment of electrical synapses enhances synchronous spiking in the mouse cerebellar cortex

International audienceIn the cerebellar cortex, molecular layer interneurons use chemical and electrical synapses to form subnetworks that fine-tune the spiking output of the cerebellum. Although electrical synapses can entrain activity within neuronal assemblies, their role in feed-forward circuits is less well explored. By combining whole-cell patch-clamp and 2-photon laser scanning microscopy of basket cells (BCs), we found that classical excitatory postsynaptic currents (EPSCs) are followed by GABA A receptor-independent outward currents, reflecting the hyperpolarization component of spikelets (a synapse-evoked action potential passively propagating from electrically coupled neighbors). FF recruitment of the spikelet-mediated inhibition curtails the integration time window of concomitant excitatory postsynaptic potentials (EPSPs) and dampens their temporal integration. In contrast with GABAergic-mediated feed-forward inhibition, the depolarizing component of spikelets transiently increases the peak amplitude of EPSPs, and thus postsynaptic spiking probability. Therefore, spikelet transmission can propagate within the BC network to generate synchronous inhibition of Purkinje cells, which can entrain cerebellar output for driving temporally precise behaviors

Modulation of Glutamate Mobility Reveals the Mechanism Underlying Slow-Rising AMPAR EPSCs and the Diffusion Coefficient in the Synaptic Cleft

AbstractFast- and slow-rising AMPA receptor-mediated EPSCs occur at central synapses. Fast-rising EPSCs are thought to be mediated by rapid local release of glutamate. However, two controversial mechanisms have been proposed to underlie slow-rising EPSCs: prolonged local release of transmitter via a fusion pore, and spillover of transmitter released rapidly from distant sites. We have investigated the mechanism underlying slow-rising EPSCs and the diffusion coefficient of glutamate in the synaptic cleft (Dglut) at cerebellar mossy fiber-granule cell synapses using a combination of diffusion modeling and patch-clamp recording. Simulations show that modulating Dglut has different effects on the peak amplitudes and time courses of EPSCs mediated by these two mechanisms. Slowing diffusion with the macromolecule dextran slowed slow-rising EPSCs and had little effect on their amplitude, indicating that glutamate spillover underlies these currents. Our results also suggest that under control conditions Dglut is approximately 3-fold lower than in free solution