Differential Effects of SNAP-25 Deletion on Ca2+-Dependent and Ca2+-Independent Neurotransmission

2007 ◽  
Vol 98 (2) ◽  
pp. 794-806 ◽  
Author(s):  
Peter Bronk ◽  
Ferenc Deák ◽  
Michael C. Wilson ◽  
Xinran Liu ◽  
Thomas C. Südhof ◽  
...  
Keyword(s):  
Neurotransmitter Release ◽  
High Frequency Stimulation ◽  
Neuronal Cultures ◽  
Inhibitory Neurotransmitter ◽  
Calcium Dependent ◽  
Receptor Complexes ◽  
Readily Releasable Pool ◽  
Protein Receptor ◽  
Frequency Stimulation ◽  
Hypertonic Stimulation

At the synapse, SNAP-25, along with syntaxin/HPC-1 and synaptobrevin/VAMP, forms SNARE N-ethylmaleimide-sensitive factor [soluble (NSF) attachment protein receptor] complexes that are thought to catalyze membrane fusion. Results from neuronal cultures of synaptobrevin-2 knockout (KO) mice showed that loss of synaptobrevin has a more severe effect on calcium-evoked release than on spontaneous release or on release evoked by hypertonicity. In this study, we recorded neurotransmitter release from neuronal cultures of SNAP-25 KO mice to determine whether they share this property. In neurons lacking SNAP-25, as those deficient in synaptobrevin-2, we found that ∼10–12% of calcium-independent excitatory and inhibitory neurotransmitter release persisted. However, in contrast to synaptobrevin-2 knockouts, this remaining readily releasable pool in SNAP-25-deficient synapses was virtually insensitive to calcium-dependent–evoked stimulation. Although field stimulation reliably evoked neurotransmitter release in synaptobrevin-2 KO neurons, responses were rare in neurons lacking SNAP-25, and unlike synaptobrevin-2–deficient synapses, SNAP-25–deficient synapses did not exhibit facilitation of release during high-frequency stimulation. This severe loss of evoked exocytosis was matched by a reduction, but not a complete loss, of endocytosis during evoked stimulation. Moreover, synaptic vesicle turnover probed by FM-dye uptake and release during hypertonic stimulation was relatively unaffected by the absence of SNAP-25. This last difference indicates that in contrast to synaptobrevin, SNAP-25 does not directly function in endocytosis. Together, these results suggest that SNAP-25 has a more significant role in calcium-secretion coupling than synaptobrevin-2.

Neurotransmitter release from high-frequency stimulation of the subthalamic nucleus

2004 ◽  
Vol 101 (3) ◽  
pp. 511-517 ◽  
Author(s):  
Kendall H. Lee ◽  
Su-Youne Chang ◽  
David W. Roberts ◽  
Uhnoh Kim
Keyword(s):  
Action Potential ◽  
High Frequency ◽  
Neurotransmitter Release ◽  
High Frequency Stimulation ◽  
Content Type ◽  
Action Potential Frequency ◽  
Frequency Stimulation ◽  
Potential Frequency ◽  
Fine Print ◽  
Stimulation Of

Object. High-frequency stimulation (HFS) delivered through implanted electrodes in the subthalamic nucleus (STN) has become an established treatment for Parkinson disease (PD). The precise mechanism of action of deep brain stimulation (DBS) in the STN is unknown, however. In the present study, the authors tested the hypothesis that HFS within the STN changes neuronal action potential firing rates during the stimulation period by modifying neurotransmitter release. Methods. Intracellular electrophysiological recordings were obtained using sharp electrodes in rat STN neurons in an in vitro slice preparation. A concentric bipolar stimulating electrode was placed in the STN slice, and electrical stimulation (pulse width 50–100 µsec, duration 100–2000 µsec, amplitude 10–500 µA, and frequency 10–200 Hz) was delivered while simultaneously obtaining intracellular recordings from an STN neuron. High-frequency stimulation of the STN either generated excitatory postsynaptic potentials (EPSPs) and increased the action potential frequency or it generated inhibitory postsynaptic potentials and decreased the action potential frequency of neurons within the STN. These effects were blocked after antagonists to glutamate and γ-aminobutyric acid were applied to the tissue slice, indicating that HFS resulted in the release of neurotransmitters. Intracellular recordings from substantia nigra pars compacta (SNc) dopaminergic neurons during HFS of the STN revealed increased generation of EPSPs and increased frequency of action potentials in SNc neurons. Conclusions. During HFS of STN neurons the mechanism of DBS may involve the release of neurotransmitters rather than the primary electrogenic inhibition of neurons.

scholarly journals Quantitative analysis of the native presynaptic cytomatrix by cryoelectron tomography

2010 ◽  
Vol 188 (1) ◽  
pp. 145-156 ◽  
Author(s):  
Rubén Fernández-Busnadiego ◽  
Benoît Zuber ◽  
Ulrike Elisabeth Maurer ◽  
Marek Cyrklaff ◽  
Wolfgang Baumeister ◽  
...  
Keyword(s):  
Synaptic Vesicle ◽  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Attachment Protein ◽  
Readily Releasable Pool ◽  
Protein Receptor ◽  
Membrane Contact ◽  
Synaptic Vesicle Release ◽  
Protein Attachment

The presynaptic terminal contains a complex network of filaments whose precise organization and functions are not yet understood. The cryoelectron tomography experiments reported in this study indicate that these structures play a prominent role in synaptic vesicle release. Docked synaptic vesicles did not make membrane to membrane contact with the active zone but were instead linked to it by tethers of different length. Our observations are consistent with an exocytosis model in which vesicles are first anchored by long (>5 nm) tethers that give way to multiple short tethers once vesicles enter the readily releasable pool. The formation of short tethers was inhibited by tetanus toxin, indicating that it depends on soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor complex assembly. Vesicles were extensively interlinked via a set of connectors that underwent profound rearrangements upon synaptic stimulation and okadaic acid treatment, suggesting a role of these connectors in synaptic vesicle mobilization and neurotransmitter release.

scholarly journals Frequency-dependent mobilization of heterogeneous pools of synaptic vesicles shapes presynaptic plasticity

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Frédéric Doussau ◽  
Hartmut Schmidt ◽  
Kevin Dorgans ◽  
Antoine M Valera ◽  
Bernard Poulain ◽  
...  
Keyword(s):  
Synaptic Vesicles ◽  
Granule Cells ◽  
Low Frequency ◽  
Synaptic Activity ◽  
High Frequency Stimulation ◽  
Frequency Dependent ◽  
Short Term Plasticity ◽  
Readily Releasable Pool ◽  
Frequency Stimulation ◽  
Sensorimotor Information

The segregation of the readily releasable pool of synaptic vesicles (RRP) in sub-pools that are differentially poised for exocytosis shapes short-term plasticity. However, the frequency-dependent mobilization of these sub-pools is poorly understood. Using slice recordings and modeling of synaptic activity at cerebellar granule cell to Purkinje cell synapses of mice, we describe two sub-pools in the RRP that can be differentially recruited upon ultrafast changes in the stimulation frequency. We show that at low-frequency stimulations, a first sub-pool is gradually silenced, leading to full blockage of synaptic transmission. Conversely, a second pool of synaptic vesicles that cannot be released by a single stimulus is recruited within milliseconds by high-frequency stimulation and support an ultrafast recovery of neurotransmitter release after low-frequency depression. This frequency-dependent mobilization or silencing of sub-pools in the RRP in terminals of granule cells may play a role in the filtering of sensorimotor information in the cerebellum.

Changes in the Readily Releasable Pool of Transmitter and in Efficacy of Release Induced by High-Frequency Firing at Aplysia Sensorimotor Synapses in Culture

2004 ◽  
Vol 91 (4) ◽  
pp. 1500-1509 ◽  
Author(s):  
Yali Zhao ◽  
Marc Klein
Keyword(s):  
Motor Neuron ◽  
High Frequency ◽  
Transmitter Release ◽  
Action Potentials ◽  
High Frequency Stimulation ◽  
Hypertonic Solution ◽  
Posttetanic Potentiation ◽  
Releasable Pool ◽  
Readily Releasable Pool ◽  
Frequency Stimulation

Synaptic transmission at the sensory neuron-motor neuron synapses of Aplysia, like transmission at many synapses of both vertebrates and invertebrates, is increased after a short burst of high-frequency stimulation (HFS), a phenomenon known as posttetanic potentiation (PTP). PTP is generally attributable to an increase in transmitter release from presynaptic neurons. We investigated whether changes in the readily releasable pool of transmitter (RRP) contribute to the potentiation that follows HFS. We compared the changes in excitatory postsynaptic potentials (EPSPs) evoked with action potentials to changes in the RRP as estimated from the asynchronous transmitter release elicited by a hypertonic solution. The changes in the EPSP were correlated with changes in the RRP, but the changes matched quantitatively only at connections whose initial synaptic strength was greater than the median for all experiments. At weaker connections, the increase in the RRP was insufficient to account for PTP. Weaker connections initially released a smaller fraction of the RRP with each EPSP than stronger ones, and this fraction increased at weaker connections after HFS. Moreover, the initial transmitter release in response to the hypertonic solution was accelerated after HFS, indicating that the increase in the efficacy of release was not restricted to excitation-secretion coupling. Modulation of the RRP and of the efficacy of release thus both contribute to the enhancement of transmitter release by HFS.

scholarly journals A frequency-dependent mobilization of heterogeneous pools of synaptic vesicles shapes presynaptic plasticity

2017 ◽  
Author(s):  
Frédéric Doussau ◽  
Hartmut Schmidt ◽  
Kevin Dorgans ◽  
Antoine M. Valera ◽  
Bernard Poulain ◽  
...  
Keyword(s):  
Granule Cell ◽  
Synaptic Vesicles ◽  
Low Frequency ◽  
Synaptic Activity ◽  
High Frequency Stimulation ◽  
Frequency Dependent ◽  
Readily Releasable Pool ◽  
Low Frequency Stimulation ◽  
Frequency Stimulation

ABSTRACTThe segregation of the readily releasable pool of synaptic vesicles (RRP) in sub-pool which are differentially poised for exocytosis shapes short-term plasticity at depressing synapses. Here, we used in vitro recording and modeling of synaptic activity at the facilitating mice cerebellar granule cell to Purkinje cell synapse to demonstrate the existence of two sub-pools of vesicles in the RRP that can be differentially recruited upon fast changes in the stimulation frequency. We show that upon low-frequency stimulation, a population of fully-releasable vesicles is silenced, leading to full blockage of synaptic transmission. A second population of vesicles, reluctant to release by simple stimuli, is recruited in a millisecond time scale by high-frequency stimulation to support an ultrafast recovery of neurotransmitter release after low-frequency depression. The frequency-dependent mobilization or silencing of sub-pools of vesicles in granule cell terminals should play a major role in the filtering of sensorimotor information in the cerebellum.

scholarly journals FMRP sustains presynaptic function via control of activity-dependent bulk endocytosis

2020 ◽  
Author(s):  
Katherine Bonnycastle ◽  
Peter C. Kind ◽  
Michael A. Cousin
Keyword(s):  
Mental Retardation ◽  
Fragile X Syndrome ◽  
Neuronal Activity ◽  
Neurotransmitter Release ◽  
Fragile X ◽  
High Frequency Stimulation ◽  
Neuronal Cultures ◽  
Fragile X Mental Retardation ◽  
Mental Retardation Protein ◽  
Activity Dependent

ABSTRACTSynaptic vesicle (SV) recycling is essential for the maintenance of neurotransmission, with a number of neurodevelopmental disorders linked to defects in this process. Fragile X syndrome (FXS) results from a loss of fragile X mental retardation protein (FMRP) encoded by the FMR1 gene. FMRP is an established translation repressor, however it also has translation-independent presynaptic roles, including regulation of the trafficking and function of specific ion channels. Since defects in SV recycling are exacerbated during intense neuronal activity, we investigated whether these events were disproportionately affected by the absence of FMRP. We revealed that primary neuronal cultures from a Fmr1 knockout rat model display a specific defect in activity-dependent bulk endocytosis (ADBE). ADBE is dominant during intense neuronal activity, and this defect resulted in an inability of Fmr1 knockout neurons to sustain SV recycling during trains of high frequency stimulation. Using a molecular replacement strategy, we revealed that a human FMRP interaction mutant failed to correct ADBE dysfunction in knockout neurons. Therefore, FMRP performs a key role in sustaining neurotransmitter release via selective control of the endocytosis mode, ADBE.SIGNIFICANCE STATEMENTLoss of fragile X mental retardation protein (FMRP) results in fragile X syndrome (FXS), however whether its loss has a direct role in neurotransmitter release remains a matter of debate. We demonstrate that neurons lacking FMRP display a specific defect in a mechanism that sustains neurotransmitter release during intense neuronal firing, called activity-dependent bulk endocytosis (ADBE). This discovery provides key insights into mechanisms of brain communication that occur due to loss of FMRP function. Importantly it also reveals ADBE as a potential therapeutic target to correct the circuit hyperexcitabilty observed in FXS.

scholarly journals Glycinergic Transmission in the Presence and Absence of Functional GlyT2: Lessons From the Auditory Brainstem

2021 ◽  
Vol 12 ◽  
Author(s):  
Sina E. Brill ◽  
Ayse Maraslioglu ◽  
Catharina Kurz ◽  
Florian Kramer ◽  
Martin F. Fuhr ◽  
...  
Keyword(s):  
Synaptic Cleft ◽  
Auditory Brainstem ◽  
Dominant Factor ◽  
High Frequency Stimulation ◽  
High Fidelity ◽  
Readily Releasable Pool ◽  
Medial Nucleus ◽  
Frequency Stimulation ◽  
Replenishment Kinetics

Synaptic transmission is controlled by re-uptake systems that reduce transmitter concentrations in the synaptic cleft and recycle the transmitter into presynaptic terminals. The re-uptake systems are thought to ensure cytosolic concentrations in the terminals that are sufficient for reloading empty synaptic vesicles (SVs). Genetic deletion of glycine transporter 2 (GlyT2) results in severely disrupted inhibitory neurotransmission and ultimately to death. Here we investigated the role of GlyT2 at inhibitory glycinergic synapses in the mammalian auditory brainstem. These synapses are tuned for resilience, reliability, and precision, even during sustained high-frequency stimulation when endocytosis and refilling of SVs probably contribute substantially to efficient replenishment of the readily releasable pool (RRP). Such robust synapses are formed between MNTB and LSO neurons (medial nucleus of the trapezoid body, lateral superior olive). By means of patch-clamp recordings, we assessed the synaptic performance in controls, in GlyT2 knockout mice (KOs), and upon acute pharmacological GlyT2 blockade. Via computational modeling, we calculated the reoccupation rate of empty release sites and RRP replenishment kinetics during 60-s challenge and 60-s recovery periods. Control MNTB-LSO inputs maintained high fidelity neurotransmission at 50 Hz for 60 s and recovered very efficiently from synaptic depression. During 'marathon-experiments' (30,600 stimuli in 20 min), RRP replenishment accumulated to 1,260-fold. In contrast, KO inputs featured severe impairments. For example, the input number was reduced to ~1 (vs. ~4 in controls), implying massive functional degeneration of the MNTB-LSO microcircuit and a role of GlyT2 during synapse maturation. Surprisingly, neurotransmission did not collapse completely in KOs as inputs still replenished their small RRP 80-fold upon 50 Hz | 60 s challenge. However, they totally failed to do so for extended periods. Upon acute pharmacological GlyT2 inactivation, synaptic performance remained robust, in stark contrast to KOs. RRP replenishment was 865-fold in marathon-experiments, only ~1/3 lower than in controls. Collectively, our empirical and modeling results demonstrate that GlyT2 re-uptake activity is not the dominant factor in the SV recycling pathway that imparts indefatigability to MNTB-LSO synapses. We postulate that additional glycine sources, possibly the antiporter Asc-1, contribute to RRP replenishment at these high-fidelity brainstem synapses.

scholarly journals Post-tetanic increase in the fast-releasing synaptic vesicle pool at the expense of the slowly releasing pool

2010 ◽  
Vol 136 (3) ◽  
pp. 259-272 ◽  
Author(s):  
Jae Sung Lee ◽  
Won-Kyung Ho ◽  
Suk-Ho Lee
Keyword(s):  
Synaptic Vesicles ◽  
Late Phase ◽  
High Frequency Stimulation ◽  
First Line ◽  
Pipette Solution ◽  
Readily Releasable Pool ◽  
Whole Cell Patch Clamp ◽  
Frequency Stimulation ◽  
Post Tetanic Potentiation ◽  
Vesicle Pool

Post-tetanic potentiation (PTP) at the calyx of Held synapse is caused by increases not only in release probability (Pr) but also in the readily releasable pool size estimated from a cumulative plot of excitatory post-synaptic current amplitudes (RRPcum), which contribute to the augmentation phase and the late phase of PTP, respectively. The vesicle pool dynamics underlying the latter has not been investigated, because PTP is abolished by presynaptic whole-cell patch clamp. We found that supplement of recombinant calmodulin to the presynaptic pipette solution rescued the increase in the RRPcum after high-frequency stimulation (100 Hz for 4-s duration, HFS), but not the increase in Pr. Release-competent synaptic vesicles (SVs) are heterogeneous in their releasing kinetics. To investigate post-tetanic changes of fast and slowly releasing SV pool (FRP and SRP) sizes, we estimated quantal release rates before and 40 s after HFS using the deconvolution method. After HFS, the FRP size increased by 19.1% and the SRP size decreased by 25.4%, whereas the sum of FRP and SRP sizes did not increase. Similar changes in the RRP were induced by a single long depolarizing pulse (100 ms). The post-tetanic complementary changes of FRP and SRP sizes were abolished by inhibitors of myosin II or myosin light chain kinase. The post-tetanic increase in the FRP size coupled to a decrease in the SRP size provides the first line of evidence for the idea that a slowly releasing SV can be converted to a fast releasing one.

scholarly journals Loss of Doc2b does not influence transmission at Purkinje cell to deep nuclei synapses under physiological conditions

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Mehak M Khan ◽  
Wade G Regehr
Keyword(s):  
Calcium Binding ◽  
Neurotransmitter Release ◽  
Time Course ◽  
Cultured Cells ◽  
Cerebellar Nuclei ◽  
High Frequency Stimulation ◽  
Physiological Conditions ◽  
Sustained Activity ◽  
Frequency Stimulation

Doc2a and Doc2b are high-affinity calcium-binding proteins that interact with SNARE proteins and phospholipids. Experiments performed on cultured cells indicated that Doc2 proteins promote spontaneous vesicle fusion and asynchronous neurotransmitter release, regulate vesicle priming, mediate augmentation, and regulate transmission during sustained activity. Here, we assess the role of Doc2 proteins in synaptic transmission under physiological conditions at mature synapses made by Purkinje cells onto neurons in the deep cerebellar nuclei (PC to DCN synapses). PCs express Doc2b but not Doc2a. Surprisingly, spontaneous neurotransmitter release, synaptic strength, the time course of evoked release, responses evoked by sustained high-frequency stimulation, and short-term plasticity were normal in Doc2b KO mice. Thus, in stark contrast to numerous functions previously proposed for Doc2, here we find that Doc2b removal does not influence transmission at PC-to-DCN synapses, indicating that conclusions based on studies of Doc2b in cultured cells do not necessarily generalize to mature synapses under physiological conditions.

scholarly journals ICAN (TRPM4) Contributes to the Intrinsic Excitability of Prefrontal Cortex Layer 2/3 Pyramidal Neurons

2021 ◽  
Vol 22 (10) ◽  
pp. 5268
Author(s):  
Francisco Andres Peralta ◽  
Denise Andres Riquelme ◽  
Franco Dario Navarro ◽  
Claudio Moreno ◽  
Elias Leiva-Salcedo
Keyword(s):  
Prefrontal Cortex ◽  
Membrane Potential ◽  
High Frequency ◽  
Pyramidal Neurons ◽  
Intrinsic Excitability ◽  
High Frequency Stimulation ◽  
Dependent Manner ◽  
Calcium Dependent ◽  
Layer 2 ◽  
Frequency Stimulation

Pyramidal neurons in the medial prefrontal cortical layer 2/3 are an essential contributor to the cellular basis of working memory; thus, changes in their intrinsic excitability critically affect medial prefrontal cortex (mPFC) functional properties. Transient Receptor Potential Melastatin 4 (TRPM4), a calcium-activated nonselective cation channel (CAN), regulates the membrane potential in a calcium-dependent manner. In this study, we uncovered the role of TRPM4 in regulating the intrinsic excitability plasticity of pyramidal neurons in the mouse mPFC layer of 2/3 using a combination of conventional and nystatin perforated whole-cell recordings. Interestingly, we found that TRPM4 is open at resting membrane potential, and its inhibition increases input resistance and hyperpolarizes membrane potential. After high-frequency stimulation, pyramidal neurons increase a calcium-activated non-selective cation current, increase the action potential firing, and the amplitude of the afterdepolarization, these effects depend on intracellular calcium. Furthermore, pharmacological inhibition or genetic silencing of TRPM4 reduces the firing rate and the afterdepolarization after high frequency stimulation. Together, these results show that TRPM4 plays a significant role in the excitability of mPFC layer 2/3 pyramidal neurons by modulating neuronal excitability in a calcium-dependent manner.

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