scholarly journals Q-SNARE Syntaxin 7 confers actin-dependent rapidly replenishing synaptic vesicles upon high activity

2020 ◽  
Author(s):  
Yasunori Mori ◽  
Koichiro Takenaka ◽  
Yugo Fukazawa ◽  
Shigeo Takamori
Keyword(s):  
High Frequency ◽  
Transmitter Release ◽  
Synaptic Vesicles ◽  
Hippocampal Neurons ◽  
Actin Polymerization ◽  
Repetitive Stimulation ◽  
Snare Proteins ◽  
Endosomal Membrane ◽  
Kinetics Of ◽  
Cultured Hippocampal Neurons

AbstractReplenishment of readily releasable synaptic vesicles (SVs) with vesicles in the recycling pool is important for sustained transmitter release during repetitive stimulation. Kinetics of replenishment and available pool size define synaptic performance. However, whether all SVs in the recycling pool are recruited for release with equal probability is unknown. Here, using comprehensive optical imaging for various presynaptic endosomal SNARE proteins in cultured hippocampal neurons, we demonstrate that part of the recycling pool bearing the endosomal Q–SNARE Syntaxin 7 (Stx7) is preferentially mobilized for release during high–frequency repetitive stimulation. Recruitment of the SV pool marked with the Stx7–reporter requires high intra–terminal Ca2+ concentrations and actin polymerization. Furthermore, disruption of Stx7 function by overexpressing the N–terminal domain selectively abolished this pool. Thus, our data indicate that endosomal membrane fusion involving Stx7 is essential for adaptation of synapses to respond high-frequency repetitive stimulation.

scholarly journals The endosomal Q-SNARE, Syntaxin 7, defines a rapidly replenishing synaptic vesicle recycling pool in hippocampal neurons

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Yasunori Mori ◽  
Koh-ichiro Takenaka ◽  
Yugo Fukazawa ◽  
Shigeo Takamori
Keyword(s):  
Membrane Fusion ◽  
High Frequency ◽  
Hippocampal Neurons ◽  
Actin Polymerization ◽  
Release Kinetics ◽  
Repetitive Stimulation ◽  
Presynaptic Terminals ◽  
Endosomal Membrane ◽  
Vesicle Recycling ◽  
Calmodulin Signaling

AbstractUpon the arrival of repetitive stimulation at the presynaptic terminals of neurons, replenishment of readily releasable synaptic vesicles (SVs) with vesicles in the recycling pool is important for sustained neurotransmitter release. Kinetics of replenishment and the available pool size define synaptic performance. However, whether all SVs in the recycling pool are recruited for release with equal probability and speed is unknown. Here, based on comprehensive optical imaging of various presynaptic endosomal SNARE proteins in cultured hippocampal neurons, all of which are implicated in organellar membrane fusion in non-neuronal cells, we show that part of the recycling pool bearing the endosomal Q-SNARE, syntaxin 7 (Stx7), is preferentially mobilized for release during high-frequency repetitive stimulation. Recruitment of the SV pool marked with an Stx7-reporter requires actin polymerization, as well as activation of the Ca2+/calmodulin signaling pathway, reminiscent of rapidly replenishing SVs characterized previously in calyx of Held synapses. Furthermore, disruption of Stx7 function by overexpressing its N-terminal domain selectively abolished this pool. Thus, our data indicate that endosomal membrane fusion involving Stx7 forms rapidly replenishing vesicles essential for synaptic responses to high-frequency repetitive stimulation, and also highlight functional diversities of endosomal SNAREs in generating distinct exocytic vesicles in the presynaptic terminals.

Dynamics of Excitatory Transmitter Release: Analysis of Synaptic Responses in CA3 Hippocampal Neurons After Repetitive Stimulation of Afferent Fibers

1998 ◽  
Vol 79 (4) ◽  
pp. 1977-1988 ◽  
Author(s):  
Marco Canepari ◽  
Enrico Cherubini
Keyword(s):  
Transmitter Release ◽  
Hippocampal Neurons ◽  
Repetitive Stimulation ◽  
Patch Clamp Technique ◽  
Afferent Fibers ◽  
Presynaptic Mechanisms ◽  
Release Analysis ◽  
Excitatory Transmitter ◽  
Stimulation Of ◽  
Synaptic Responses

Canepari, Marco and Enrico Cherubini. Dynamics of excitatory transmitter release: analysis of synaptic responses in CA3 hippocampal neurons after repetitive stimulation of afferent fibers. J. Neurophysiol. 79: 1977–1988, 1998. The patch-clamp technique (whole cell configuration) was used to record excitatory postsynaptic currents (EPSCs) evoked by repetitive stimulation (4 pulses at 50-ms intervals) of afferent fibers in the stratum lucidum-radiatum. Different synaptic behaviors (EPSC patterns) were classified in terms of facilitation or depression of the mean amplitude of the second, third, and fourth EPSC with respect to the previous one. A large variety of EPSC patterns was observed by stimulating different afferent fibers. Experiments with the mGluR2/mGluR3 agonist 2-(2,3-dicarboxycyclopropyl)glycine (DCG-IV) (1 μM), a compound that reduces release at mossy but not at associative commissural fibers and therefore allows to identify the origin of synaptic responses, showed that particular EPSC patterns could not be associated to the activation of a specific type of synaptic input. To investigate the role of the probability of release in the dynamics of synaptic activity, the extracellular calcium concentration was varied from 0.8 to 4 mM in several experiments. EPSC patterns dominated by depression, characteristics of high release probability conditions, could be observed in the majority of the cases in the presence of higher calcium concentrations. A quantitative model for dynamics of transmitter release has been developed. Experimental results were compared with data computed with the model taking into account the probability of release and the time course of reavailability. This work indicates that short-term changes of presynaptic conditions occurring during a train of action potentials can account for the high variability of EPSC responses. The model that is proposed also suggests a general method of experimental data analysis to investigate the possible presynaptic mechanisms underlying long-lasting changes in synaptic efficacy.

scholarly journals Dual pools of actin at presynaptic terminals

2012 ◽  
Vol 107 (12) ◽  
pp. 3479-3492 ◽  
Author(s):  
Adam Bleckert ◽  
Huzefa Photowala ◽  
Simon Alford
Keyword(s):  
Synaptic Transmission ◽  
Synaptic Vesicle ◽  
Synaptic Vesicles ◽  
Repetitive Stimulation ◽  
Filamentous Actin ◽  
Cortical Actin ◽  
Vesicle Recycling ◽  
Latrunculin A ◽  
Kinetics Of

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.

Role of Presynaptic L-Type Ca2+ Channels in GABAergic Synaptic Transmission in Cultured Hippocampal Neurons

1999 ◽  
Vol 81 (3) ◽  
pp. 1225-1230 ◽  
Author(s):  
Kimmo Jensen ◽  
Morten Skovgaard Jensen ◽  
John D. C. Lambert
Keyword(s):  
Synaptic Transmission ◽  
Transmitter Release ◽  
Hippocampal Neurons ◽  
Low Frequency ◽  
Tetanic Stimulation ◽  
Vesicle Release ◽  
Gabaergic Synaptic Transmission ◽  
Cultured Hippocampal Neurons ◽  
40 Hz

Role of presynaptic L-type Ca2+ channels in GABAergic synaptic transmission in cultured hippocampal neurons. Using dual whole cell patch-clamp recordings of monosynaptic GABAergic inhibitory postsynaptic currents (IPSCs) in cultured rat hippocampal neurons, we have previously demonstrated posttetanic potentiation (PTP) of IPSCs. Tetanic stimulation of the GABAergic neuron leads to accumulation of Ca2+ in the presynaptic terminals. This enhances the probability of GABA-vesicle release for up to 1 min, which underlies PTP. In the present study, we have examined the effect of altering the probability of release on PTP of IPSCs. Baclofen (10 μM), which depresses presynaptic Ca2+ entry through N- and P/Q-type voltage-dependent Ca2+ channels (VDCCs), caused a threefold greater enhancement of PTP than did reducing [Ca2+]o to 1.2 mM, which causes a nonspecific reduction in Ca2+ entry. This finding prompted us to investigate whether presynaptic L-type VDCCs contribute to the Ca2+ accumulation in the boutons during spike activity. The L-type VDCC antagonist, nifedipine (10 μM), had no effect on single IPSCs evoked at 0.2 Hz but reduced the PTP evoked by a train of 40 Hz for 2 s by 60%. Another L-type VDCC antagonist, isradipine (5 μM), similarly inhibited PTP by 65%. Both L-type VDCC blockers also depressed IPSCs during the stimulation (i.e., they increased tetanic depression). The L-type VDCC “agonist” (−)BayK 8644 (4 μM) had no effect on PTP evoked by a train of 40 Hz for 2 s, which probably saturated the PTP process, but enhanced PTP evoked by a train of 1 s by 91%. In conclusion, the results indicate that L-type VDCCs do not participate in low-frequency synchronous transmitter release, but contribute to presynaptic Ca2+ accumulation during high-frequency activity. This helps maintain vesicle release during tetanic stimulation and also enhances the probability of transmitter release during the posttetanic period, which is manifest as PTP. Involvement of L-type channels in these processes represents a novel presynaptic regulatory mechanism at fast CNS synapses.

Distinct Initial SNARE Configurations Underlying the Diversity of Exocytosis

2012 ◽  
Vol 92 (4) ◽  
pp. 1915-1964 ◽  
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.

scholarly journals Facilitation versus depression in cultured hippocampal neurons determined by targeting of Ca2+ channel Cavβ4 versus Cavβ2 subunits to synaptic terminals

2007 ◽  
Vol 178 (3) ◽  
pp. 489-502 ◽  
Author(s):  
Mian Xie ◽  
Xiang Li ◽  
Jing Han ◽  
Daniel L. Vogt ◽  
Silke Wittemann ◽  
...  
Keyword(s):  
Transmitter Release ◽  
Hippocampal Neurons ◽  
Presynaptic Terminal ◽  
Paired Pulse ◽  
Physiological Properties ◽  
Specific Manner ◽  
A Subunit ◽  
Synaptic Distribution ◽  
Ca2 Channels ◽  
Cultured Hippocampal Neurons

Ca2+ channel β subunits determine the transport and physiological properties of high voltage–activated Ca2+ channel complexes. Our analysis of the distribution of the Cavβ subunit family members in hippocampal neurons correlates their synaptic distribution with their involvement in transmitter release. We find that exogenously expressed Cavβ4b and Cavβ2a subunits distribute in clusters and localize to synapses, whereas Cavβ1b and Cavβ3 are homogenously distributed. According to their localization, Cavβ2a and Cavβ4b subunits modulate the synaptic plasticity of autaptic hippocampal neurons (i.e., Cavβ2a induces depression, whereas Cavβ4b induces paired-pulse facilitation [PPF] followed by synaptic depression during longer stimuli trains). The induction of PPF by Cavβ4b correlates with a reduction in the release probability and cooperativity of the transmitter release. These results suggest that Cavβ subunits determine the gating properties of the presynaptic Ca2+ channels within the presynaptic terminal in a subunit-specific manner and may be involved in organization of the Ca2+ channel relative to the release machinery.

Sign in / Sign up

Export Citation Format

Share Document