Merits and Limitations of Vesicle Pool Models in View of Heterogeneous Populations of Synaptic Vesicles

We used synaptophysin-pHluorin expressed in hippocampal neurons to address how functional properties of terminals, namely, evoked release, total vesicle pool size, and release fraction, vary spatially across individual axon arbors. Consistent with previous reports, over short arbor distances (∼100 μm), evoked release was spatially heterogeneous when terminals contacted different postsynaptic dendrites or neurons. Regardless of the postsynaptic configuration, the evoked release and total vesicle pool size spatially covaried, suggesting that the fraction of synaptic vesicles available for release (release fraction) was similar over short distances. Evoked release and total vesicle pool size were highly correlated with the amount of NMDA receptors and PSD-95 in postsynaptic specialization. However, when individual axons were followed over longer distances (several hundred micrometers), a significant increase in evoked release was observed distally that was associated with an increased release fraction in distal terminals. The increase in distal release fraction can be accounted for by changes in individual vesicle release probability as well as readily releasable pool size. Our results suggest that for a single axon arbor, presynaptic strength indicated by evoked release over short distances is correlated with heterogeneity in total vesicle pool size, whereas over longer distances presynaptic strength is correlated with the spatial modulation of release fraction. Thus the mechanisms that determine synaptic strength differ depending on spatial scale.

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Genetic evidence for an equilibrium between docked and undocked vesicles

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.1999.0381 ◽

1999 ◽

Vol 354 (1381) ◽

pp. 299-306 ◽

Cited By ~ 24

Author(s):

Jing Li ◽

Thomas L. Schwarz

Keyword(s):

Synaptic Transmission ◽

Nerve Terminal ◽

Synaptic Vesicles ◽

Genetic Evidence ◽

Temperature Dependent ◽

Vesicle Pool

By using the shibire mutation to block endocytosis in a temperature–dependent fashion, we have manipulated the number of synaptic vesicles in a nerve terminal and have observed a remarkable proportionality of the number of quanta released to the size of the total vesicle pool. In the experiments described below we determine that approximately 0.3% of the vesicle pool is released per stimulus. The data suggest that the pool of readily releasable docked vesicles does not represent the saturation of a limiting number of release sites, but instead represents a subset of vesicles that is in equilibrium with the larger pool of vesicles. Before presenting this data and the significance of the finding for the regulation of neurotransmission, we will briefly review the use of Drosophila genetics as a tool for dissecting synaptic transmission.

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RNA editing of CAPS1 regulates synaptic vesicle organization, release and retrieval

10.1101/178202 ◽

2017 ◽

Cited By ~ 1

Author(s):

Randi J. Ulbricht ◽

Sarah J. Sun ◽

Claire E. DelBove ◽

Kristina E. Kitko ◽

Saad C. Rehman ◽

...

Keyword(s):

Rna Editing ◽

Neurotransmitter Release ◽

Synaptic Vesicles ◽

Hippocampal Neurons ◽

Protein Isoforms ◽

Editing Event ◽

Calcium Dependent ◽

Presynaptic Vesicle ◽

Vesicle Pool ◽

Fine Tune

ABSTRACTCalcium-dependent activator protein for secretion 1 (CAPS1) facilitates the docking and priming of synaptic and dense core vesicles. A conserved hairpin structure in the CAPS1 pre-mRNA allows an post-transcriptional adenosine-to-inosine RNA editing event to alter a genomically-encoded glutamate to a glycine codon. Functional comparisons of CAPS1 protein isoforms in primary hippocampal neurons show that elevation of edited CAPS1 isoforms facilitates presynaptic vesicle clustering and turnover. Conversely, non-edited CAPS1 isoforms slow evoked release, increase spontaneous fusion, and loosen the clustering of synaptic vesicles. Therefore, CAPS1 editing promotes organization of the vesicle pool in a way that is beneficial for evoked release, while non-edited isoforms promote more lax vesicle organization that widens distribution, attenuates evoked release and eases the control of spontaneous fusion. Overall, RNA editing of CAPS1 is a mechanism to fine tune neurotransmitter release.IMPACT STATEMENTPost-transcriptional RNA editing of CAPS1 is a mechanism to regulate neurotransmitter release from synaptic vesicles.

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Roles of ATP in Depletion and Replenishment of the Releasable Pool of Synaptic Vesicles

Journal of Neurophysiology ◽

10.1152/jn.2002.88.1.98 ◽

2002 ◽

Vol 88 (1) ◽

pp. 98-106 ◽

Cited By ~ 52

Author(s):

Ruth Heidelberger ◽

Peter Sterling ◽

Gary Matthews

Keyword(s):

Synaptic Vesicles ◽

Atp Hydrolysis ◽

Synaptic Ribbons ◽

Calcium Dependent ◽

Releasable Pool ◽

Synaptic Terminals ◽

Active Zones ◽

Vesicle Movement ◽

Vesicle Pool ◽

Secretory Apparatus

Synaptic terminals of retinal bipolar neurons contain a pool of readily releasable synaptic vesicles that undergo rapid calcium-dependent release. ATP hydrolysis is required for the functional refilling of this vesicle pool. However, it was unclear which steps required ATP hydrolysis: delivery of vesicles to their anatomical release sites or preparation of synaptic vesicles and/or the secretory apparatus for fusion. To address this, we dialyzed single synaptic terminals with ATP or the poorly hydrolyzable analogue ATP-γS and examined the size of the releasable pool, refilling of the releasable pool, and the number of vesicles at anatomical active zones. After minutes of dialysis with ATP-γS, vesicles already in the releasable pool could still be discharged. This pool was not functionally refilled despite the fact that its anatomical correlate, the number of synaptic vesicles tethered to active zone synaptic ribbons, was completely normal. We conclude 1) because the existing releasable pool is stable during prolonged inhibition of ATP hydrolysis, whereas entry into the functional pool is blocked, a vesicle on entering the pool will tend to remain there until it fuses; 2) because the anatomical pool is unaffected by inhibition of ATP hydrolysis, failure to refill the functional pool is not caused by failure of vesicle movement; 3) local vesicle movements important for pool refilling and fusion are independent of conventional ATP-dependent motor proteins; and 4) ATP hydrolysis is required for the biochemical transition of vesicles and/or release sites to fusion-competent status.

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The Same Synaptic Vesicles Originate Synchronous and Asynchronous Transmitter Release

Acta Naturae ◽

10.32607/20758251-2015-7-3-81-88 ◽

2015 ◽

Vol 7 (3) ◽

pp. 81-88 ◽

Cited By ~ 2

Author(s):

P. N. Grigoryev ◽

A. L. Zefirov

Keyword(s):

Synaptic Vesicle ◽

High Frequency ◽

Transmitter Release ◽

Synaptic Vesicles ◽

High Frequency Stimulation ◽

Vesicle Pools ◽

Bivalent Cations ◽

Frequency Stimulation ◽

Nerve Muscle ◽

Vesicle Pool

Transmitter release and synaptic vesicle exo- and endocytosis during high-frequency stimulation (20 pulses/s) in the extracellular presence of different bivalent cations (Ca2+, Sr2+ or Ba2+) were studied in frog cutaneous pectoris nerve-muscle preparations. It was shown in electrophysiological experiments that almost only synchronous transmitter release was registered in a Ca2+-containing solution; a high intensity of both synchronous and asynchronous transmitter release was registered in a Sr2+-containing solution, and asynchronous transmitter release almost only was observed in a Ba2+-containing solution. It was shown in experiments with a FM 1-43 fluorescent dye that the synaptic vesicles that undergo exocytosis-endocytosis during synchronous transmitter release (Ca-solutions) are able to participate in asynchronous exocytosis in Ba-solutions. The vesicles that had participated in the asynchronous transmitter release (Ba-solutions) could subsequently participate in a synchronous release (Ca-solutions). It was shown in experiments with isolated staining of recycling and reserve synaptic vesicle pools that both types of evoked transmitter release originate from the same synaptic vesicle pool.

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Actin-dependent rapid recruitment of reluctant synaptic vesicles into a fast-releasing vesicle pool

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1114072109 ◽

2012 ◽

Vol 109 (13) ◽

pp. E765-E774 ◽

Cited By ~ 53

Author(s):

J. S. Lee ◽

W.-K. Ho ◽

S.-H. Lee

Keyword(s):

Synaptic Vesicles ◽

Vesicle Pool

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Role of Drosophila Rab5 during endosomal trafficking at the synapse and evoked neurotransmitter release

The Journal of Cell Biology ◽

10.1083/jcb.200211087 ◽

2003 ◽

Vol 161 (3) ◽

pp. 609-624 ◽

Cited By ~ 283

Author(s):

Tanja Wucherpfennig ◽

Michaela Wilsch-Bräuninger ◽

Marcos González-Gaitán

Keyword(s):

Neurotransmitter Release ◽

Synaptic Vesicles ◽

Small Gtpase ◽

Endosomal Trafficking ◽

Neuromuscular Synapses ◽

Endosomal Compartment ◽

Trafficking Pathway ◽

Vesicular Membrane ◽

Vesicle Pool

During constitutive endocytosis, internalized membrane traffics through endosomal compartments. At synapses, endocytosis of vesicular membrane is temporally coupled to action potential–induced exocytosis of synaptic vesicles. Endocytosed membrane may immediately be reused for a new round of neurotransmitter release without trafficking through an endosomal compartment. Using GFP-tagged endosomal markers, we monitored an endosomal compartment in Drosophila neuromuscular synapses. We showed that in conditions in which the synaptic vesicles pool is depleted, the endosome is also drastically reduced and only recovers from membrane derived by dynamin-mediated endocytosis. This suggests that membrane exchange takes place between the vesicle pool and the synaptic endosome. We demonstrate that the small GTPase Rab5 is required for endosome integrity in the presynaptic terminal. Impaired Rab5 function affects endo- and exocytosis rates and decreases the evoked neurotransmitter release probability. Conversely, Rab5 overexpression increases the release efficacy. Therefore, the Rab5-dependent trafficking pathway plays an important role for synaptic performance.

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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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