Kinetics of Releasable Synaptic Vesicles and Their Plastic Changes at Hippocampal Mossy Fiber Synapses

We investigated actin's function in vesicle recycling and exocytosis at lamprey synapses and show that FM1-43 puncta and phalloidin-labeled filamentous actin (F-actin) structures are colocalized, yet recycling vesicles are not contained within F-actin clusters. Additionally, phalloidin also labels a plasma membrane-associated cortical actin. Injection of fluorescent G-actin revealed activity-independent dynamic actin incorporation into presynaptic synaptic vesicle clusters but not into cortical actin. Latrunculin-A, which sequesters G-actin, dispersed vesicle-associated actin structures and prevented subsequent labeled G-actin and phalloidin accumulation at presynaptic puncta, yet cortical phalloidin labeling persisted. Dispersal of presynaptic F-actin structures by latrunculin-A did not disrupt vesicle clustering or recycling or alter the amplitude or kinetics of excitatory postsynaptic currents (EPSCs). However, it slightly enhanced release during repetitive stimulation. While dispersal of presynaptic actin puncta with latrunculin-A failed to disperse synaptic vesicles or inhibit synaptic transmission, presynaptic phalloidin injection blocked exocytosis and reduced endocytosis measured by action potential-evoked FM1-43 staining. Furthermore, phalloidin stabilization of only cortical actin following pretreatment with latrunculin-A was sufficient to inhibit synaptic transmission. Conversely, treatment of axons with jasplakinolide, which induces F-actin accumulation but disrupts F-actin structures in vivo, resulted in increased synaptic transmission accompanied by a loss of phalloidin labeling of cortical actin but no loss of actin labeling within vesicle clusters. Marked synaptic deficits seen with phalloidin stabilization of cortical F-actin, in contrast to the minimal effects of disruption of a synaptic vesicle-associated F-actin, led us to conclude that two structurally and functionally distinct pools of actin exist at presynaptic sites.

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Distinct Initial SNARE Configurations Underlying the Diversity of Exocytosis

Physiological Reviews ◽

10.1152/physrev.00007.2012 ◽

2012 ◽

Vol 92 (4) ◽

pp. 1915-1964 ◽

Cited By ~ 93

Author(s):

Haruo Kasai ◽

Noriko Takahashi ◽

Hiroshi Tokumaru

Keyword(s):

Membrane Trafficking ◽

Synaptic Vesicles ◽

Cell Types ◽

Snare Proteins ◽

Attachment Protein ◽

Protein Receptor ◽

Large Dense Core Vesicles ◽

Sensitive Factor ◽

The Common ◽

Kinetics Of

The dynamics of exocytosis are diverse and have been optimized for the functions of synapses and a wide variety of cell types. For example, the kinetics of exocytosis varies by more than five orders of magnitude between ultrafast exocytosis in synaptic vesicles and slow exocytosis in large dense-core vesicles. However, in all cases, exocytosis is mediated by the same fundamental mechanism, i.e., the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. It is often assumed that vesicles need to be docked at the plasma membrane and SNARE proteins must be preassembled before exocytosis is triggered. However, this model cannot account for the dynamics of exocytosis recently reported in synapses and other cells. For example, vesicles undergo exocytosis without prestimulus docking during tonic exocytosis of synaptic vesicles in the active zone. In addition, epithelial and hematopoietic cells utilize cAMP and kinases to trigger slow exocytosis of nondocked vesicles. In this review, we summarize the manner in which the diversity of exocytosis reflects the initial configurations of SNARE assembly, including trans-SNARE, binary-SNARE, unitary-SNARE, and cis-SNARE configurations. The initial SNARE configurations depend on the particular SNARE subtype (syntaxin, SNAP25, or VAMP), priming proteins (Munc18, Munc13, CAPS, complexin, or snapin), triggering proteins (synaptotagmins, Doc2, and various protein kinases), and the submembraneous cytomatrix, and they are the key to determining the kinetics of subsequent exocytosis. These distinct initial configurations will help us clarify the common SNARE assembly processes underlying exocytosis and membrane trafficking in eukaryotic cells.

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Decision letter: RIM-BP2 primes synaptic vesicles via recruitment of Munc13-1 at hippocampal mossy fiber synapses

10.7554/elife.43243.029 ◽

2018 ◽

Author(s):

Craig Curtis Garner

Keyword(s):

Synaptic Vesicles ◽

Mossy Fiber

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Kinetics of cation-induced aggregation of Torpedo electric organ synaptic vesicles

Biochimica et Biophysica Acta (BBA) - Biomembranes ◽

10.1016/0005-2736(79)90332-8 ◽

1979 ◽

Vol 557 (2) ◽

pp. 340-353 ◽

Cited By ~ 17

Author(s):

Duncan H. Haynes ◽

Jeffry Lansman ◽

Anne L. Cahill ◽

Stephen J. Morris

Keyword(s):

Synaptic Vesicles ◽

Electric Organ ◽

Torpedo Electric Organ ◽

Induced Aggregation ◽

Kinetics Of

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Determinants of Synaptobrevin Regulation in Membranes

Molecular Biology of the Cell ◽

10.1091/mbc.e07-01-0049 ◽

2007 ◽

Vol 18 (6) ◽

pp. 2037-2046 ◽

Cited By ~ 44

Author(s):

Tabrez J. Siddiqui ◽

Olga Vites ◽

Alexander Stein ◽

Rainer Heintzmann ◽

Reinhard Jahn ◽

...

Keyword(s):

Synaptic Vesicles ◽

Snare Complex ◽

Fusion Activity ◽

Transmembrane Region ◽

Complex Assembly ◽

Overall Stability ◽

Snare Motif ◽

Linker Domain ◽

Kinetics Of ◽

Constitutively Active

Neuronal exocytosis is driven by the formation of SNARE complexes between synaptobrevin 2 on synaptic vesicles and SNAP-25/syntaxin 1 on the plasma membrane. It has remained controversial, however, whether SNAREs are constitutively active or whether they are down-regulated until fusion is triggered. We now show that synaptobrevin in proteoliposomes as well as in purified synaptic vesicles is constitutively active. Potential regulators such as calmodulin or synaptophysin do not affect SNARE activity. Substitution or deletion of residues in the linker connecting the SNARE motif and transmembrane region did not alter the kinetics of SNARE complex assembly or of SNARE-mediated fusion of liposomes. Remarkably, deletion of C-terminal residues of the SNARE motif strongly reduced fusion activity, although the overall stability of the complexes was not affected. We conclude that although complete zippering of the SNARE complex is essential for membrane fusion, the structure of the adjacent linker domain is less critical, suggesting that complete SNARE complex assembly not only connects membranes but also drives fusion.

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A comparative morphometric study of synaptic vesicles and other organelles in mossy fiber endings of the pigeon and the rat

Cells Tissues Organs ◽

10.1159/000144931 ◽

1978 ◽

Vol 100 (4) ◽

pp. 471-477 ◽

Cited By ~ 4

Author(s):

M.M. Paula-Barbosa ◽

M.A. Sobrinho-Simões ◽

R. Faria

Keyword(s):

Synaptic Vesicles ◽

Mossy Fiber ◽

Morphometric Study

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The Architecture of the Active Zone in the Presynaptic Nerve Terminal

Physiology ◽

10.1152/physiol.00014.2004 ◽

2004 ◽

Vol 19 (5) ◽

pp. 262-270 ◽

Cited By ~ 149

Author(s):

R. Grace Zhai ◽

Hugo J. Bellen

Keyword(s):

Active Zone ◽

Synaptic Vesicles ◽

Molecular Organization ◽

Nerve Terminals ◽

Presynaptic Nerve Terminal ◽

Structural Differences ◽

Common Principle ◽

Active Zones ◽

Presynaptic Nerve Terminals ◽

Kinetics Of

Active zones are highly specialized sites for release of neurotransmitter from presynaptic nerve terminals. The architecture of the active zone is exquisitely designed to facilitate the regulated tethering, docking, and fusing of the synaptic vesicles with the plasma membrane. Here we present our view of the structural and molecular organization of active zones across species and propose that all active zones are organized according to a common principle in which the structural differences correlate with the kinetics of transmitter release.

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Zinc-Induced Augmentation of Excitatory Synaptic Currents and Glutamate Receptor Responses in Hippocampal CA3 Neurons

Journal of Neurophysiology ◽

10.1152/jn.2001.85.3.1185 ◽

2001 ◽

Vol 85 (3) ◽

pp. 1185-1196 ◽

Cited By ~ 51

Author(s):

Dean D. Lin ◽

Akiva S. Cohen ◽

Douglas A. Coulter

Keyword(s):

Pyramidal Neurons ◽

Granule Cells ◽

Mossy Fiber ◽

Release Kinetics ◽

Excitatory Synapses ◽

Hippocampal Ca3 ◽

Excitatory Neurotransmission ◽

High Concentrations ◽

Ca3 Neurons ◽

Kinetics Of

Zinc is found throughout the CNS at synapses co-localized with glutamate in presynaptic terminals. In particular, dentate granule cells' (DGC) mossy fiber (MF) axons contain especially high concentrations of zinc co-localized with glutamate within vesicles. To study possible physiological roles of zinc, visualized slice-patch techniques were used to voltage-clamp rat CA3 pyramidal neurons, and miniature excitatory postsynaptic currents (mEPSCs) were isolated. Bath-applied zinc (200 μM) enhanced median mEPSC peak amplitudes to 153.0% of controls, without affecting mEPSC kinetics. To characterize this augmentation further, rapid agonist application was performed on perisomatic outside-out patches to coapply zinc with glutamate extremely rapidly for brief (1 ms) durations, thereby emulating release kinetics of these substances at excitatory synapses. When zinc was coapplied with glutamate, zinc augmented peak glutamate currents (mean ± SE, 116.6 ± 2.8% and 143.8 ± 9.8% of controls at 50 and 200 μM zinc, respectively). This zinc-induced potentiation was concentration dependent, and pharmacological isolation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor–mediated currents (AMPAR currents) gave results similar to those observed with glutamate application (mean, 115.0 ± 5.4% and 132.5 ± 9.1% of controls at 50 and 200 μM zinc, respectively). Inclusion of the AMPAR desensitization blocker cyclothiazide in the control solution, however, abolished zinc-induced augmentation of glutamate-evoked currents, suggesting that zinc may potentiate AMPAR currents by inhibiting AMPAR desensitization. Based on the results of the present study, we hypothesize that zinc is a powerful modulator of both excitatory synaptic transmission and glutamate-evoked currents at physiologically relevant concentrations. This modulatory role played by zinc may be a significant factor in enhancing excitatory neurotransmission and could significantly regulate function at the mossy fiber-CA3 synapse.

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Synaptic integration in a model of cerebellar granule cells

Journal of Neurophysiology ◽

10.1152/jn.1994.72.2.999 ◽

1994 ◽

Vol 72 (2) ◽

pp. 999-1009 ◽

Cited By ~ 149

Author(s):

F. Gabbiani ◽

J. Midtgaard ◽

T. Knopfel

Keyword(s):

Action Potential ◽

Granule Cell ◽

Granule Cells ◽

Mossy Fiber ◽

Potassium Conductance ◽

Time Interval ◽

Synaptic Current ◽

Action Potential Firing ◽

Potential Firing ◽

Kinetics Of

1. We have developed a compartmental model of a turtle cerebellar granule cell consisting of 13 compartmentds that represent the soma and 4 dendrites. We used this model to investigate the synaptic integration of mossy fiber inputs in granule cells. 2. The somatic compartment contained six active ionic conductances: a sodium conductance with fast activation and inactivation kinetics, gNa; a high-voltage-activated calcium conductance, gCa(HVA); a delayed potassium conductance, gK(DR); a transient potassium conductance, gK(A); a slowly relaxing mixed Na+/K+ conductance activating at hyperpolarized membrane potentials, gH, and a calcium- and voltage-dependent potassium conductance, gK(Ca). The kinetics of these conductances was derived from electrophysiological studies in a variety of preparations, including turtle and rat granule cells. 3. In the soma, dynamics of intracellular free Ca2+ was modeled by incorporation of a Na+/Ca2+ exchanger, radial diffusion, and binding sites for Ca2+. 4. The model of the turtle granule cell exhibited depolarization-induced action potential firing with properties closely resembling those seen with intracellular recordings in turtle granule cells in vitro. 5. In the most distal compartments of the dendrites, mossy fiber activity induced synaptic currents mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)- and N-methyl-D-aspartate (NMDA)-type of glutamate receptors. The strength of synaptic inputs chosen was such that the synaptic potential induced by synchronous activation of two mossy fiber synapses reached threshold for induction of a single action potential. 6. The slow time course of the NMDA synaptic current together with the slow relaxation kinetics of gH significantly affected the temporal summation of excitatory synaptic potentials. A priming action potential evoked by mossy fiber stimulation increased the maximal time interval between two synaptic potentials capable to reach again threshold for a subsequent action potential. This time interval then decreased in parallel with the decay of the NMDA synaptic current, reached a minimum after 200 ms, and slowly recovered with reactivation of gH. 7. Repetitive, steady activation of synaptic conductances by a single mossy fiber at different frequencies induced action potential firing with a sharp threshold at 12 Hz. Activity of a single or of several mossy fibers induced firing of the granule cell at a frequency close to that induced when the average synaptic current was directly injected into the cell. The mossy fiber activity-granule cell firing frequency curve was close to linear with a slope of about one-half for input frequencies < or = 400 Hz.(ABSTRACT TRUNCATED AT 400 WORDS)

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