scholarly journals Calcium dependence of neurotransmitter release at a high fidelity synapse

2021 ◽  
Author(s):  
Abdelmoneim Eshra ◽  
Hartmut Schmidt ◽  
Jens Eilers ◽  
Stefan Hallermann
Keyword(s):  
Synaptic Plasticity ◽  
Release Rate ◽  
High Frequency ◽  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Mossy Fiber ◽  
High Fidelity ◽  
Fundamental Parameters ◽  
High Affinity ◽  
Vesicle Pools

The Ca2+-dependence of the recruitment, priming, and fusion 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 because disentangling recruitment, priming, and fusion of vesicles is technically challenging. Here, we investigated the Ca2+-sensitivity of these steps at cerebellar mossy fiber synapses, which are characterized by fast vesicle recruitment 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. Sustained vesicle recruitment was Ca2+-independent. Finally, quantitative mechanistic release schemes with five Ca2+ binding steps incorporating rapid vesicle recruitment via parallel or sequential vesicle pools could explain our data. We thus show that co-existing high and low-affinity Ca2+ sensors mediate recruitment, priming, and fusion of synaptic vesicles at a high-fidelity synapse.

scholarly journals Calcium dependence of neurotransmitter release at a high fidelity synapse

eLife ◽  
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.

scholarly journals Postsynaptic Neuroligin-1 Mediates Presynaptic Endocytosis During Neuronal Activity

2021 ◽  
Vol 14 ◽  
Author(s):  
Jiaqi Keith Luo ◽  
Holly Melland ◽  
Jess Nithianantharajah ◽  
Sarah L. Gordon
Keyword(s):  
Ampa Receptors ◽  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
High Fidelity ◽  
Excitatory Synapses ◽  
Synaptic Efficacy ◽  
Molecular Architecture ◽  
Adhesion Protein ◽  
Presynaptic Nerve Terminal ◽  
Presynaptic Release

Fast, high-fidelity neurotransmission and synaptic efficacy requires tightly regulated coordination of pre- and postsynaptic compartments and alignment of presynaptic release sites with postsynaptic receptor nanodomains. Neuroligin-1 (Nlgn1) is a postsynaptic cell-adhesion protein exclusively localised to excitatory synapses that is crucial for coordinating the transsynaptic alignment of presynaptic release sites with postsynaptic AMPA receptors as well as postsynaptic transmission and plasticity. However, little is understood about whether the postsynaptic machinery can mediate the molecular architecture and activity of the presynaptic nerve terminal, and thus it remains unclear whether there are presynaptic contributions to Nlgn1-dependent control of signalling and plasticity. Here, we employed a presynaptic reporter of neurotransmitter release and synaptic vesicle dynamics, synaptophysin-pHluorin (sypHy), to directly assess the presynaptic impact of loss of Nlgn1. We show that lack of Nlgn1 had no effect on the size of the readily releasable or entire recycling pool of synaptic vesicles, nor did it impact exocytosis. However, we observed significant changes in the retrieval of synaptic vesicles by compensatory endocytosis, specifically during activity. Our data extends growing evidence that synaptic adhesion molecules critical for forming transsynaptic scaffolds are also important for regulating activity-induced endocytosis at the presynapse.

scholarly journals Bassoon controls synaptic vesicle pools via regulation of presynaptic phosphorylation and cAMP homeostasis

2021 ◽  
Author(s):  
Carolina Montenegro-Venegas ◽  
Debarpan Guhathakurta ◽  
Eneko Pina-Fernandez ◽  
Maria Andres-Alonso ◽  
Florian Plattner ◽  
...  
Keyword(s):  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Molecular Mechanisms ◽  
Cultured Neurons ◽  
Glutamatergic Synapses ◽  
Vesicle Pools ◽  
Downstream Effectors ◽  
Synapsin 1

Neuronal presynaptic terminals contain hundreds of neurotransmitter-filled synaptic vesicles (SVs). The morphologically uniform SVs differ in their release competence segregating into functional pools that differentially contribute to neurotransmission. The presynaptic scaffold bassoon is required for neurotransmission, but the underlying molecular mechanisms are unknown. We report that glutamatergic synapses lacking bassoon featured a decreased SV release competence and increased resting pool of SV as observed by imaging of SV release in cultured neurons. Further analyses in vitro and in vivo revealed a dysregulation of CDK5/calcineurin and cAMP/PKA presynaptic signalling resulting in an aberrant phosphorylation of their downstream effectors synapsin 1 and SNAP25, which are well-known regulators of SV release competence. An acute pharmacological restoration of physiological CDK5 and cAMP/PKA activity fully normalised the SV pools in neurons lacking bassoon. Finally, we demonstrated that CDK5-dependent regulation of PDE4 activity controls SV release competence by interaction with cAMP/PKA signalling. These data reveal that bassoon organises SV pools via regulation of presynaptic phosphorylation and indicate an involvement of PDE4 in the control of neurotransmitter release.

scholarly journals RIM-BP2 primes synaptic vesicles via recruitment of Munc13-1 at hippocampal mossy fiber synapses

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Marisa M Brockmann ◽  
Marta Maglione ◽  
Claudia G Willmes ◽  
Alexander Stumpf ◽  
Boris A Bouazza ◽  
...  
Keyword(s):  
Active Zone ◽  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Mossy Fiber ◽  
Substantial Impact ◽  
Vesicle Docking ◽  
Vesicular Release ◽  
Anatomical Properties ◽  
Presynaptic Protein ◽  
Determinant Factor

All synapses require fusion-competent vesicles and coordinated Ca2+-secretion coupling for neurotransmission, yet functional and anatomical properties are diverse across different synapse types. We show that the presynaptic protein RIM-BP2 has diversified functions in neurotransmitter release at different central murine synapses and thus contributes to synaptic diversity. At hippocampal pyramidal CA3-CA1 synapses, RIM-BP2 loss has a mild effect on neurotransmitter release, by only regulating Ca2+-secretion coupling. However, at hippocampal mossy fiber synapses, RIM-BP2 has a substantial impact on neurotransmitter release by promoting vesicle docking/priming and vesicular release probability via stabilization of Munc13-1 at the active zone. We suggest that differences in the active zone organization may dictate the role a protein plays in synaptic transmission and that differences in active zone architecture is a major determinant factor in the functional diversity of synapses.

scholarly journals Fast resupply of synaptic vesicles requires Synaptotagmin-3

2021 ◽  
Author(s):  
Dennis J. Weingarten ◽  
Amita Shrestha ◽  
Sarah A. Kissiwaa ◽  
Evan Spruston ◽  
Skyler L. Jackman
Keyword(s):  
Synaptic Transmission ◽  
High Frequency ◽  
Synaptic Vesicles ◽  
Critical Role ◽  
Neuronal Firing ◽  
Probability Models ◽  
Short Term ◽  
Vesicle Docking ◽  
High Affinity ◽  
Readily Releasable Pool

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.

scholarly journals Reduced endogenous Ca2+ buffering speeds active zone Ca2+ signaling

2015 ◽  
Vol 112 (23) ◽  
pp. E3075-E3084 ◽  
Author(s):  
Igor Delvendahl ◽  
Lukasz Jablonski ◽  
Carolin Baade ◽  
Victor Matveev ◽  
Erwin Neher ◽  
...  
Keyword(s):  
High Resolution ◽  
Synaptic Transmission ◽  
Active Zone ◽  
Neurotransmitter Release ◽  
Mossy Fiber ◽  
Repetitive Firing ◽  
Two Photon ◽  
High Affinity ◽  
Model Predictions ◽  
Active Zones

Fast synchronous neurotransmitter release at the presynaptic active zone is triggered by local Ca2+ signals, which are confined in their spatiotemporal extent by endogenous Ca2+ buffers. However, it remains elusive how rapid and reliable Ca2+ signaling can be sustained during repetitive release. Here, we established quantitative two-photon Ca2+ imaging in cerebellar mossy fiber boutons, which fire at exceptionally high rates. We show that endogenous fixed buffers have a surprisingly low Ca2+-binding ratio (∼15) and low affinity, whereas mobile buffers have high affinity. Experimentally constrained modeling revealed that the low endogenous buffering promotes fast clearance of Ca2+ from the active zone during repetitive firing. Measuring Ca2+ signals at different distances from active zones with ultra-high-resolution confirmed our model predictions. Our results lead to the concept that reduced Ca2+ buffering enables fast active zone Ca2+ signaling, suggesting that the strength of endogenous Ca2+ buffering limits the rate of synchronous synaptic transmission.

Evidence for NMDA and mGlu Receptor-Dependent Long-Term Potentiation of Mossy Fiber–Granule Cell Transmission in Rat Cerebellum

1999 ◽  
Vol 81 (1) ◽  
pp. 277-287 ◽  
Author(s):  
Egidio D'Angelo ◽  
Paola Rossi ◽  
Simona Armano ◽  
Vanni Taglietti
Keyword(s):  
Synaptic Plasticity ◽  
Nmda Receptor ◽  
Granule Cell ◽  
High Frequency ◽  
Mossy Fiber ◽  
Long Term Potentiation ◽  
Mglu Receptor ◽  
Rat Cerebellum ◽  
Term Potentiation

D'Angelo, Egidio, Paola Rossi, Simona Armano, and Vanni Taglietti. Evidence for NMDA and mGlu receptor-dependent long-term potentiation of mossy fiber–granule cell transmission in rat cerebellum. J. Neurophysiol. 81: 277–287, 1999. Long-term potentiation (LTP) is a form of synaptic plasticity that can be revealed at numerous hippocampal and neocortical synapses following high-frequency activation of N-methyl-d-aspartate (NMDA) receptors. However, it was not known whether LTP could be induced at the mossy fiber–granule cell relay of cerebellum. This is a particularly interesting issue because theories of the cerebellum do not consider or even explicitly negate the existence of mossy fiber–granule cell synaptic plasticity. Here we show that high-frequency mossy fiber stimulation paired with granule cell membrane depolarization (−40 mV) leads to LTP of granule cell excitatory postsynaptic currents (EPSCs). Pairing with a relatively hyperpolarized potential (−60 mV) or in the presence of NMDA receptor blockers [5-amino-d-phosphonovaleric acid (APV) and 7-chloro-kynurenic acid (7-Cl-Kyn)] prevented LTP, suggesting that the induction process involves a voltage-dependent NMDA receptor activation. Metabotropic glutamate receptors were also involved because blocking them with (+)-α-methyl-4-carboxyphenyl-glycine (MCPG) prevented potentiation. At the cytoplasmic level, EPSC potentiation required a Ca2+ increase and protein kinase C (PKC) activation. Potentiation was expressed through an increase in both the NMDA and non-NMDA receptor-mediated current and by an NMDA current slowdown, suggesting that complex mechanisms control synaptic efficacy during LTP. LTP at the mossy fiber–granule cell synapse provides the cerebellar network with a large reservoir for memory storage, which may be needed to optimize pattern recognition and, ultimately, cerebellar learning and computation.

The Same Synaptic Vesicles Originate Synchronous and Asynchronous Transmitter Release

Acta Naturae ◽  
2015 ◽  
Vol 7 (3) ◽  
pp. 81-88 ◽  
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.

scholarly journals Postsynaptic neuroligin-1 mediates presynaptic endocytosis during neuronal activity

2021 ◽  
Author(s):  
Jiaqi Keith Luo ◽  
Holly Melland ◽  
Jess Nithianantharajah ◽  
Sarah L Gordon
Keyword(s):  
Ampa Receptors ◽  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
High Fidelity ◽  
Excitatory Synapses ◽  
Synaptic Efficacy ◽  
Molecular Architecture ◽  
Adhesion Protein ◽  
Presynaptic Nerve Terminal ◽  
Presynaptic Release

Fast, high-fidelity neurotransmission and synaptic efficacy requires tightly regulated coordination of pre- and postsynaptic compartments and alignment of presynaptic release sites with postsynaptic receptor nanodomains. Neuroligin-1 (Nlgn-1) is a postsynaptic cell-adhesion protein exclusively localised to excitatory synapses that is crucial for coordinating the transsynaptic alignment of presynaptic release sites with postsynaptic AMPA receptors as well as postsynaptic transmission and plasticity. However, little is understood about whether the postsynaptic machinery can mediate the molecular architecture and activity of the presynaptic nerve terminal, and thus it remains unclear whether there are presynaptic contributions to Nlgn1-dependent control of signalling and plasticity. Here, we employed a presynaptic reporter of neurotransmitter release and synaptic vesicle dynamics, synaptophysin-pHluorin (sypHy), to directly assess the presynaptic impact of loss of Nlgn1. We show that lack of Nlgn1 had no effect on the size of the readily releasable or entire recycling pool of synaptic vesicles, nor did it impact exocytosis. However, we observed significant changes in the retrieval of synaptic vesicles by compensatory endocytosis, specifically during activity. Our data extends growing evidence that synaptic adhesion molecules critical for forming transsynaptic scaffolds are also important for regulating activity-induced endocytosis at the presynapse.

scholarly journals Synapse-specific and compartmentalized expression of presynaptic homeostatic potentiation

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Xiling Li ◽  
Pragya Goel ◽  
Catherine Chen ◽  
Varun Angajala ◽  
Xun Chen ◽  
...  
Keyword(s):  
Synaptic Plasticity ◽  
Neuromuscular Junction ◽  
Motor Neuron ◽  
Neurotransmitter Release ◽  
Genetic Manipulation ◽  
Receptor Expression ◽  
Homeostatic Plasticity ◽  
Postsynaptic Receptor ◽  
Vesicle Pools ◽  
Synaptic Structures

Postsynaptic compartments can be specifically modulated during various forms of synaptic plasticity, but it is unclear whether this precision is shared at presynaptic terminals. Presynaptic homeostatic plasticity (PHP) stabilizes neurotransmission at the Drosophila neuromuscular junction, where a retrograde enhancement of presynaptic neurotransmitter release compensates for diminished postsynaptic receptor functionality. To test the specificity of PHP induction and expression, we have developed a genetic manipulation to reduce postsynaptic receptor expression at one of the two muscles innervated by a single motor neuron. We find that PHP can be induced and expressed at a subset of synapses, over both acute and chronic time scales, without influencing transmission at adjacent release sites. Further, homeostatic modulations to CaMKII, vesicle pools, and functional release sites are compartmentalized and do not spread to neighboring pre- or post-synaptic structures. Thus, both PHP induction and expression mechanisms are locally transmitted and restricted to specific synaptic compartments.

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