Fast resupply of synaptic vesicles requires Synaptotagmin-3

AbstractSustained neuronal activity demands quick resupply of synaptic vesicles in order to maintain reliable synaptic transmission. Such vesicle replenishment is accelerated by sub-micromolar presynaptic Ca2+ signals by an as yet unidentified high-affinity Ca2+ sensor1-4. Here we identify a novel presynaptic role for the high-affinity Ca2+ sensor Synaptotagmin-3 (SYT3)5 in driving vesicle replenishment and short-term synaptic plasticity. Synapses in Syt3 knockout mice exhibit enhanced short-term depression, and recovery is slower and insensitive to presynaptic residual Ca2+. During sustained neuronal firing, SYT3 speeds vesicle replenishment and increases the size of the readily releasable pool of vesicles. SYT3 also mediates a second form of short-term enhancement called facilitation, under conditions of low vesicle release probability. Models of vesicle trafficking suggest that SYT3 could combat synaptic depression by accelerating vesicle docking at active zones. Our results reveal a critical role for presynaptic SYT3 in maintaining reliable high-frequency synaptic transmission in neural circuits.

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Activity and cytosolic Na+ regulates synaptic vesicle endocytosis

10.1101/2019.12.27.889790 ◽

2019 ◽

Author(s):

Yun Zhu ◽

Dainan Li ◽

Hai Huang

Keyword(s):

Synaptic Transmission ◽

High Frequency ◽

Synaptic Vesicles ◽

Glutamate Uptake ◽

High Frequencies ◽

Vesicle Recycling ◽

Two Photon ◽

Readily Releasable Pool ◽

Content Change ◽

Intracellular Ca

ABSTRACTRetrieval of synaptic vesicles via endocytosis is essential for maintaining sustained synaptic transmission, especially for neurons that fire action potentials at high frequencies. However, how activity regulates synaptic vesicles recycling is largely unknown. Here we report that Na+ substantially accumulated in the mouse calyx of Held terminals during repetitive high-frequency spiking. Elevated presynaptic Na+ accelerated both slow and rapid forms of endocytosis and facilitated endocytosis overshoot but did not affect the readily releasable pool size, Ca2+ influx, or exocytosis. To examine whether this facilitation of endocytosis is related to the Na+-dependent vesicular content change, we dialyzed increasing concentrations of glutamate into the presynaptic cytosol or blocked the vesicular glutamate uptake with bafilomycin and found the rate of endocytosis was not affected by regulating the glutamate content in the presynaptic terminal. Endocytosis is critically dependent on intracellular Ca2+, and the activity of Na+/Ca2+ exchanger (NCX) may be altered when the Na+ gradient is changed. However, neither NCX blocker nor change of extracellular Na+ concentration affected the endocytosis rate. Moreover, two-photon Ca2+ imaging showed that presynaptic Na+ did not affect the action potential-evoked intracellular Ca2+ transient and decay. Therefore, we revealed a novel mechanism of cytosolic Na+ in accelerating vesicle endocytosis. During high-frequency synaptic transmission, when large amounts of synaptic vesicles are fused, Na+ accumulated in terminals, facilitated vesicle recycling and sustained reliable synaptic transmission.

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KCNQ/Kv7 Channel Regulation of Hippocampal Gamma-Frequency Firing in the Absence of Synaptic Transmission

Journal of Neurophysiology ◽

10.1152/jn.01083.2005 ◽

2006 ◽

Vol 95 (5) ◽

pp. 3105-3112 ◽

Cited By ~ 11

Author(s):

S. Piccinin ◽

A. D. Randall ◽

J. T. Brown

Keyword(s):

Synaptic Transmission ◽

High Frequency ◽

Epileptiform Activity ◽

Hippocampal Slices ◽

Neuronal Firing ◽

Population Spike ◽

Channel Blockers ◽

Kv7 Channels ◽

Population Spikes ◽

Gamma Frequency

Synchronous neuronal firing can be induced in hippocampal slices in the absence of synaptic transmission by lowering extracellular Ca2+ and raising extracellular K+. However, the ionic mechanisms underlying this nonsynaptic synchronous firing are not well understood. In this study we have investigated the role of KCNQ /Kv7 channels in regulating this form of nonsynaptic bursting activity. Incubation of rat hippocampal slices in reduced (<0.2 mM) [Ca2+]o and increased (6.3 mM) [K+]o, blocked synaptic transmission, increased neuronal firing, and led to the development of spontaneous periodic nonsynaptic epileptiform activity. This activity was recorded extracellularly as large (4.7 ± 1.9 mV) depolarizing envelopes with superimposed high-frequency synchronous population spikes. These intraburst population spikes initially occurred at a high frequency (about 120 Hz), which decayed throughout the burst stabilizing in the gamma-frequency band (30–80 Hz). Further increasing [K+]o resulted in an increase in the interburst frequency without altering the intraburst population spike frequency. Application of retigabine (10 μM), a Kv7 channel modulator, completely abolished the bursts, in an XE-991–sensitive manner. Furthermore, application of the Kv7 channel blockers, linopirdine (10 μM) or XE-991 (10 μM) alone, abolished the gamma frequency, but not the higher-frequency population spike firing observed during low Ca2+/high K+ bursts. These data suggest that Kv7 channels are likely to play a role in the regulation of synchronous population firing activity.

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A Simple Depletion Model of the Readily Releasable Pool of Synaptic Vesicles Cannot Account for Paired-Pulse Depression

Journal of Neurophysiology ◽

10.1152/jn.00554.2006 ◽

2007 ◽

Vol 97 (1) ◽

pp. 948-950 ◽

Cited By ~ 10

Author(s):

Jane M. Sullivan

Keyword(s):

Synaptic Vesicles ◽

Hippocampal Neurons ◽

Synaptic Activity ◽

Excitatory Synapses ◽

Short Term ◽

Paired Pulse ◽

Short Term Plasticity ◽

Releasable Pool ◽

Readily Releasable Pool ◽

Paired Pulse Depression

Paired-pulse depression (PPD) is a form of short-term plasticity that plays a central role in processing of synaptic activity and is manifest as a decrease in the size of the response to the second of two closely timed stimuli. Despite mounting evidence to the contrary, PPD is still commonly thought to reflect depletion of the pool of synaptic vesicles available for release in response to the second stimulus. Here it is shown that PPD cannot be accounted for by depletion at excitatory synapses made by hippocampal neurons because PPD is unaffected by changes in the fraction of the readily releasable pool (RRP) released by the first of a pair of pulses.

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Ca2+/Calmodulin and Presynaptic Short-Term Plasticity

ISRN Neurology ◽

10.5402/2011/919043 ◽

2011 ◽

Vol 2011 ◽

pp. 1-7 ◽

Cited By ~ 7

Author(s):

Sumiko Mochida

Keyword(s):

Transmitter Release ◽

Presynaptic Terminal ◽

Neuronal Firing ◽

Firing Activity ◽

Short Term ◽

Short Term Plasticity ◽

Readily Releasable Pool ◽

Ef Hand ◽

Sensor Protein ◽

Activity Dependent

Synaptic efficacy is remodeled by neuronal firing activity at the presynaptic terminal. Presynaptic activity-dependent changes in transmitter release induce postsynaptic plasticity, including morphological change in spine, gene transcription, and protein synthesis and trafficking. The presynaptic transmitter release is triggered and regulated by Ca2+, which enters through voltage-gated Ca2+ (CaV) channels and diffuses into the presynaptic terminal accompanying action potential firings. Residual Ca2+ is sensed by Ca2+-binding proteins, among other potential actions, it mediates time- and space-dependent synaptic facilitation and depression via effects on CaV2 channel gating and vesicle replenishment in the readily releasable pool (RRP). Calmodulin, a Ca2+-sensor protein with an EF-hand motif that binds Ca2+, interacts with CaV2 channels and autoreceptors in modulation of SNARE-mediated exocytosis.

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Interactions Between Asynchronous Release and Short-Term Plasticity in the Nucleus Accumbens Slice

Journal of Neurophysiology ◽

10.1152/jn.01149.2005 ◽

2006 ◽

Vol 95 (3) ◽

pp. 2020-2023 ◽

Cited By ~ 14

Author(s):

Gregory O. Hjelmstad

Keyword(s):

Nucleus Accumbens ◽

Synaptic Transmission ◽

Short Term ◽

Short Term Plasticity ◽

Releasable Pool ◽

Readily Releasable Pool ◽

Glutamate Synapses ◽

Asynchronous Release

Glutamate synapses in the nucleus accumbens (NAc) display asynchronous release in response to trains of stimulation. However, it is unclear what role this asynchronous release plays in synaptic transmission in this nucleus. This process was studied, specifically looking at the interaction between short-term depression and asynchronous release. These results indicate that synchronous and asynchronous release do not compete for a depleted readily releasable pool of vesicles.

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Calcium dependence of neurotransmitter release at a high fidelity synapse

eLife ◽

10.7554/elife.70408 ◽

2021 ◽

Vol 10 ◽

Author(s):

Abdelmoneim Eshra ◽

Hartmut Schmidt ◽

Jens Eilers ◽

Stefan Hallermann

Keyword(s):

High Frequency ◽

Neurotransmitter Release ◽

Synaptic Vesicles ◽

Mossy Fiber ◽

High Fidelity ◽

Technical Challenge ◽

Fundamental Parameters ◽

High Affinity ◽

Vesicle Pools ◽

Intracellular Ca

The Ca2+-dependence of the priming, fusion, and replenishment of synaptic vesicles are fundamental parameters controlling neurotransmitter release and synaptic plasticity. Despite intense efforts, these important steps in the synaptic vesicles’ cycle remain poorly understood due to the technical challenge in disentangling vesicle priming, fusion, and replenishment. Here, we investigated the Ca2+-sensitivity of these steps at mossy fiber synapses in the rodent cerebellum, which are characterized by fast vesicle replenishment mediating high-frequency signaling. We found that the basal free Ca2+ concentration (<200 nM) critically controls action potential-evoked release, indicating a high-affinity Ca2+ sensor for vesicle priming. Ca2+ uncaging experiments revealed a surprisingly shallow and non-saturating relationship between release rate and intracellular Ca2+ concentration up to 50 μM. The rate of vesicle replenishment during sustained elevated intracellular Ca2+ concentration exhibited little Ca2+-dependence. Finally, quantitative mechanistic release schemes with five Ca2+ binding steps incorporating rapid vesicle replenishment via parallel or sequential vesicle pools could explain our data. We thus show that co-existing high- and low-affinity Ca2+ sensors mediate priming, fusion, and replenishment of synaptic vesicles at a high-fidelity synapse.

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Doc2-mediated superpriming supports synaptic augmentation

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1802104115 ◽

2018 ◽

Vol 115 (24) ◽

pp. E5605-E5613 ◽

Cited By ~ 7

Author(s):

Renhao Xue ◽

David A. Ruhl ◽

Joseph S. Briguglio ◽

Alexander G. Figueroa ◽

Robert A. Pearce ◽

...

Keyword(s):

Plasma Membrane ◽

Synaptic Plasticity ◽

Learning And Memory ◽

Synaptic Vesicles ◽

Hippocampal Neurons ◽

Underlying Mechanism ◽

Short Term ◽

Short Term Plasticity ◽

Releasable Pool ◽

Readily Releasable Pool

Various forms of synaptic plasticity underlie aspects of learning and memory. Synaptic augmentation is a form of short-term plasticity characterized by synaptic enhancement that persists for seconds following specific patterns of stimulation. The mechanisms underlying this form of plasticity are unclear but are thought to involve residual presynaptic Ca2+. Here, we report that augmentation was reduced in cultured mouse hippocampal neurons lacking the Ca2+ sensor, Doc2; other forms of short-term enhancement were unaffected. Doc2 binds Ca2+ and munc13 and translocates to the plasma membrane to drive augmentation. The underlying mechanism was not associated with changes in readily releasable pool size or Ca2+ dynamics, but rather resulted from superpriming a subset of synaptic vesicles. Hence, Doc2 forms part of the Ca2+-sensing apparatus for synaptic augmentation via a mechanism that is molecularly distinct from other forms of short-term plasticity.

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Presynaptically silent synapses are modulated by the density of surrounding astrocytes

10.1101/2020.03.20.000166 ◽

2020 ◽

Author(s):

Kohei Oyabu ◽

Kotomi Takeda ◽

Hiroyuki Kawano ◽

Kaori Kubota ◽

Takuya Watanabe ◽

...

Keyword(s):

Synaptic Transmission ◽

Synaptic Vesicles ◽

Hippocampal Neurons ◽

Cell Type ◽

Countable Number ◽

Glutamatergic Synapses ◽

Readily Releasable Pool ◽

Silent Synapses ◽

Patch Clamp Electrophysiology ◽

Lower Ratio

ABSTRACTThe astrocyte, a major glial cell type, is involved in formation and maturation of synapses, and thus contributes to sustainable synaptic transmission between neurons. Given that the animals in the higher phylogenetic tree have brains with higher density of glial cells with respect to neurons, there is a possibility that the relative astrocytic density directly influences synaptic transmission. However, the notion has not been tested thoroughly. Here we addressed it, by using a primary culture preparation where single hippocampal neurons are surrounded by a variable but countable number of cortical astrocytes in dot-patterned microislands, and recording synaptic transmission by patch-clamp electrophysiology. Neurons with a higher astrocytic density showed a higher amplitude of evoked excitatory postsynaptic current (EPSC) than that of neurons with a lower astrocytic density. The size of readily releasable pool of synaptic vesicles per neuron was significantly higher. The frequency of spontaneous synaptic transmission (miniature EPSC) was higher, but the amplitude was unchanged. The number of morphologically identified glutamatergic synapses was unchanged, but the number of functional ones was increased, indicating a lower ratio of presynaptically silent synapses. Taken together, the higher astrocytic density enhanced excitatory synaptic transmission by increasing the number of functional synapses through presynaptic un-silencing.

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microRNA-138 controls hippocampal interneuron function and short-term memory

10.1101/2021.05.12.443573 ◽

2021 ◽

Author(s):

Gerhard Schratt ◽

Reetu Daswani ◽

Carlotta Gilardi ◽

Michael Soutschek ◽

Kerstin Weiss ◽

...

Keyword(s):

Synaptic Transmission ◽

Neural Circuit ◽

Short Term Memory ◽

Critical Role ◽

Excitatory Neuron ◽

Inhibitory Interneurons ◽

Short Term ◽

Term Memory ◽

And Function ◽

Neuron Function

A tightly regulated balance between excitatory and inhibitory (E/I) synaptic transmission is critical for neural circuit assembly and function. microRNAs control excitatory neuron function, but their role in inhibitory interneurons is unknown. Here, we show that miR-138-5p regulates the expression of presynaptic genes in hippocampal parvalbumin-expressing inhibitory interneurons to control short-term memory. Our finding suggests a critical role for miR-138-5p in disorders of impaired E/I balance, such as autism and schizophrenia.

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Spike activity regulates vesicle filling at a glutamatergic synapse

10.1101/2019.12.20.873083 ◽

2019 ◽

Author(s):

Dainan Li ◽

Yun Zhu ◽

Hai Huang

Keyword(s):

Synaptic Transmission ◽

High Frequency ◽

Synaptic Vesicles ◽

Action Potentials ◽

Glutamate Uptake ◽

Signal Transmission ◽

Auditory Information ◽

High Frequency Signal ◽

Quantal Size ◽

Vesicle Pool

AbstractSynaptic vesicles need to be recycled and refilled rapidly to maintain high-frequency synaptic transmission. However, little is known about the control of transport of neurotransmitter into synaptic vesicles, which determines the contents of synaptic vesicles and the strength of synaptic transmission. Here we report that Na+ substantially accumulated in the calyx of Held terminals of mouse during high-frequency spiking. The activity-induced elevation of cytosolic Na+ activated vesicular Na+/H+ exchanger, facilitated glutamate loading into synaptic vesicles and increased quantal size of asynchronous released vesicles, but did not affect the vesicle pool size or release probability. Consequently, presynaptic Na+ increased the excitatory postsynaptic currents and was required to maintain the reliable high-frequency signal transmission from the presynaptic calyces to the postsynaptic MNTB neurons. Blocking Na+/H+ activity with EIPA decreased the postsynaptic current and caused failures in postsynaptic firing. Therefore, during high-frequency synaptic transmission, when large amounts of glutamate are released, Na+ accumulated in the terminals, activated vesicular Na+/H+ exchanger, and regulated glutamate loading as a function of the level of vesicle release.Significant statementAuditory information is encoded by action potentials phase-locked to sound frequency at high rates. Large amount of synaptic vesicles are released during high-frequency synaptic transmission, accordingly, synaptic vesicles need to be recycled and refilled rapidly. We have recently found that a Na+/H+ exchanger expressed on synaptic vesicles promotes vesicle filling with glutamate. Here we showed that during high-frequency signaling, when massive vesicles are released, Na+ accumulates in terminals and facilitates glutamate uptake into synaptic vesicle. Na+ thus accelerates vesicle replenishment and sustains reliable synaptic transmission.

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