scholarly journals Probing the segregation of evoked and spontaneous neurotransmission via photobleaching and recovery of a fluorescent glutamate sensor

2021 ◽  
Author(s):  
Camille Wang ◽  
Natali Chanaday ◽  
Lisa M Monteggia ◽  
Ege T Kavalali
Keyword(s):  
Action Potential ◽  
Fluorescent Probe ◽  
Neurotransmitter Release ◽  
Differential Effect ◽  
Glutamate Release ◽  
Neuronal Cells ◽  
Spontaneous Release ◽  
Neuronal Dendrites

Synapses maintain both action potential-evoked and spontaneous neurotransmitter release, however, organization of these two forms of release within an individual synapse remains unclear. Here, we used photobleaching properties of iGluSnFR, a fluorescent probe that detects glutamate, to investigate the subsynaptic organization of evoked and spontaneous release. In non-neuronal cells and neuronal dendrites, iGluSnFR fluorescence is intensely photobleached and recovers via diffusion of non-photobleached probes within 10-seconds. After photobleaching, while evoked iGluSnFR events could be rapidly suppressed, their recovery required several hours. In contrast, iGluSnFR responses to spontaneous release were comparatively resilient to photobleaching, unless the complete pool of iGluSnFR was activated by glutamate perfusion. This differential effect of photobleaching on different modes of neurotransmission is consistent with a subsynaptic organization where sites of evoked glutamate release are clustered and corresponding iGluSnFR probes are diffusion restricted, while spontaneous release sites are broadly spread across a synapse with readily diffusible iGluSnFR probes.

scholarly journals Axonal ER Ca2+ Release Enhances Miniature, but Reduces Activity-Dependent Glutamate Release in a Huntington Disease Model

2020 ◽  
Author(s):  
James P. Mackay ◽  
Amy I. Smith-Dijak ◽  
Ellen T. Koch ◽  
Peng Zhang ◽  
Evan Fung ◽  
...  
Keyword(s):  
Action Potential ◽  
Cortical Neurons ◽  
Neurotransmitter Release ◽  
Glutamate Release ◽  
Disease Model ◽  
Spontaneous Release ◽  
Synaptic Event ◽  
Chemical Synapses ◽  
Activity Dependent ◽  
Slow Action Potential

AbstractAction potential-independent (miniature) neurotransmission occurs at all chemical synapses, but remains poorly understood, particularly in pathological contexts. Spontaneous release of Ca2+ from the axonal endoplasmic reticulum (ER) is thought to facilitated miniature neurotransmission, and aberrant ER Ca2+ handling is notably implicated in the progression of Huntington’s disease (HD) and other neurodegenerative diseases. Here, we report elevated glutamate-mediated miniature synaptic event frequencies in YAC128 (HD-model) cortical neurons, which pharmacological experiments suggest is mediated by enhanced spontaneous ER Ca2+ release. Calcium imaging using an axon-localized sensor revealed slow action potential (AP)-independent axonal Ca2+ waves, which were more common in YAC128 cortical neurons. Conversely, spontaneous axonal ER Ca2+ release was associated with reduced AP-dependent axonal Ca2+ events and consequent glutamate release. Together, our results suggest spontaneous release of axonal ER Ca2+ stores oppositely regulates activity-dependent and -independent neurotransmitter release in HD, with potential implications for the fidelity and plasticity of cortical excitatory signaling.

Selective Inhibition of Spontaneous But Not Ca2+-Dependent Release Machinery by Presynaptic Group II mGluRs in Rat Cerebellar Slices

2006 ◽  
Vol 96 (1) ◽  
pp. 86-96 ◽  
Author(s):  
Maike Glitsch
Keyword(s):  
Action Potential ◽  
Glutamate Receptors ◽  
Neurotransmitter Release ◽  
Metabotropic Glutamate Receptors ◽  
Gaba Release ◽  
Spontaneous Release ◽  
Metabotropic Receptors ◽  
Voltage Gated ◽  
Metabotropic Glutamate ◽  
Group Ii

Two main forms of neurotransmitter release are known: action potential-evoked and spontaneous release. Action potential-evoked release depends on Ca2+entry through voltage-gated Ca2+channels, whereas spontaneous release is thought to be Ca2+-independent. Generally, spontaneous and action potential-evoked release are believed to use the same release machinery to release neurotransmitter. This study shows, using the whole cell patch-clamp technique in rat cerebellar slices, that at the interneuron- Purkinje cell synapse activation of presynaptic group II metabotropic glutamate receptors suppresses spontaneous GABA release through a mechanism independent of voltage-gated Ca2+channels, store-operated Ca2+channels, and Ca2+release from intracellular Ca2+stores, suggesting that the metabotropic receptors target the release machinery directly. Voltage gated Ca2+channel-independent release following increased presynaptic cAMP production is similarly inhibited by these metabotropic receptors. In contrast, both voltage-gated Ca2+channel-dependent and presynaptic N-methyl-d-aspartate receptor-dependent GABA release were unaffected by activation of group II metabotropic glutamate receptors. Hence, the mechanisms underlying spontaneous and Ca2+-dependent GABA release are distinct in that only the former is blocked by group II metabotropic glutamate receptors. Thus the same neurotransmitter, glutamate, can activate or inhibit neurotransmitter release by selecting different receptors that target different release machineries.

scholarly journals Early Ischemia Enhances Action Potential-Dependent, Spontaneous Glutamatergic Responses in CA1 Neurons

2009 ◽  
Vol 30 (3) ◽  
pp. 555-565 ◽  
Author(s):  
Hui Ye ◽  
Shirin Jalini ◽  
Liang Zhang ◽  
Milton Charlton ◽  
Peter L Carlen
Keyword(s):  
Action Potential ◽  
Pyramidal Neurons ◽  
Glutamate Release ◽  
Brain Slices ◽  
Spontaneous Release ◽  
Ca1 Neurons ◽  
Relative Contribution ◽  
Hippocampal Ca1 ◽  
Ca3 Neurons

Two types of quantal spontaneous neurotransmitter release are present in the nervous system, namely action potential (AP)-dependent release and AP-independent release. Previous studies have identified and characterized AP-independent release during hypoxia and ischemia. However, the relative contribution of AP-dependent spontaneous release to the overall glutamate released during transient ischemia has not been quantified. Furthermore, the neuronal activity that mediates such release has not been identified. Using acute brain slices, we show that AP-dependent release constitutes approximately one-third of the overall glutamate-mediated excitatory postsynaptic potentials/currents (EPSPs/EPSCs) measured onto hippocampal CA1 pyramidal neurons. However, during transient (2 mins) in vitro hypoxia–hypoglycemia, large-amplitude, AP-dependent spontaneous release is significantly enhanced and contributes to 74% of the overall glutamatergic responses. This increased AP-dependent release is due to hyper-excitability in the presynaptic CA3 neurons, which is mediated by the activity of NMDA receptors. Spontaneous glutamate release during ischemia can lead to excitotoxicity and perturbation of neural network functions.

Presynaptic roles of intracellular Ca2+ stores in signalling and exocytosis

2010 ◽  
Vol 38 (2) ◽  
pp. 529-535 ◽  
Author(s):  
Sohaib Nizami ◽  
Vivian W.Y. Lee ◽  
Jennifer Davies ◽  
Philip Long ◽  
Jasmina N. Jovanovic ◽  
...  
Keyword(s):  
Protein Kinases ◽  
G Protein ◽  
Nerve Terminal ◽  
Neurotransmitter Release ◽  
Glutamate Release ◽  
Neuronal Cells ◽  
Receptor Activation ◽  
Pivotal Role ◽  
Presynaptic Function ◽  
G Protein Coupled

The signalling roles of Ca2+ic (intracellular Ca2+) stores are well established in non-neuronal and neuronal cells. In neurons, although Ca2+ic stores have been assigned a pivotal role in postsynaptic responses to Gq-coupled receptors, or secondarily to extracellular Ca2+ influx, the functions of dynamic Ca2+ic stores in presynaptic terminals remain to be fully elucidated. In the present paper, we review some of the recent evidence supporting an involvement of Ca2+ic in presynaptic function, and discuss loci at which this source of Ca2+ may impinge. Nerve terminal preparations provide good models for functionally examining putative Ca2+ic stores under physiological and pathophysiological stimulation paradigms, using Ca2+-dependent activation of resident protein kinases as sensors for fine changes in intracellular Ca2+ levels. We conclude that intraterminal Ca2+ic stores may, directly or indirectly, enhance neurotransmitter release following nerve terminal depolarization and/or G-protein-coupled receptor activation. During conditions that prevail following neuronal ischaemia, increased glutamate release instigated by Ca2+ic store activation may thereby contribute to excitotoxicity and eventual synaptopathy.

scholarly journals Homeostatic synaptic depression is achieved through a regulated decrease in presynaptic calcium channel abundance

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Michael A Gaviño ◽  
Kevin J Ford ◽  
Santiago Archila ◽  
Graeme W Davis
Keyword(s):  
Synaptic Plasticity ◽  
Neuromuscular Junction ◽  
Action Potential ◽  
Calcium Channel ◽  
Neurotransmitter Release ◽  
Calcium Influx ◽  
Homeostatic Synaptic Plasticity ◽  
Action Potential Waveform ◽  
Presynaptic Calcium ◽  
Potential Waveform

Homeostatic signaling stabilizes synaptic transmission at the neuromuscular junction (NMJ) of Drosophila, mice, and human. It is believed that homeostatic signaling at the NMJ is bi-directional and considerable progress has been made identifying mechanisms underlying the homeostatic potentiation of neurotransmitter release. However, very little is understood mechanistically about the opposing process, homeostatic depression, and how bi-directional plasticity is achieved. Here, we show that homeostatic potentiation and depression can be simultaneously induced, demonstrating true bi-directional plasticity. Next, we show that mutations that block homeostatic potentiation do not alter homeostatic depression, demonstrating that these are genetically separable processes. Finally, we show that homeostatic depression is achieved by decreased presynaptic calcium channel abundance and calcium influx, changes that are independent of the presynaptic action potential waveform. Thus, we identify a novel mechanism of homeostatic synaptic plasticity and propose a model that can account for the observed bi-directional, homeostatic control of presynaptic neurotransmitter release.

Endogenous Amino Acid Release from Cultured Cerebellar Neuronal Cells: Effect of Tetanus Toxin on Glutamate Release

1989 ◽  
Vol 52 (4) ◽  
pp. 1229-1239 ◽  
Author(s):  
Bernard J. Vliet ◽  
Michèle Sebben ◽  
Aline Dumuis ◽  
Jacqueline Gabrion ◽  
Joël Bockaert ◽  
...  
Keyword(s):  
Amino Acid ◽  
Tetanus Toxin ◽  
Glutamate Release ◽  
Neuronal Cells ◽  
Amino Acid Release ◽  
Acid Release ◽  
Endogenous Amino Acid

Fractionation of the motor unit: response to tetanus

1961 ◽  
Vol 200 (4) ◽  
pp. 689-693
Author(s):  
Simeon Locke
Keyword(s):  
Action Potential ◽  
Motor Unit ◽  
Nerve Terminal ◽  
Differential Effect ◽  
Blocking Agent ◽  
Single Motor Unit ◽  
Single Motor ◽  
Blocking Agents ◽  
Before And After ◽  
Post Tetanic Potentiation

The effect of a tetanus on the motor unit of the gastrocnemius of the rat has been studied before and after administration of blocking agents. Post-tetanic potentiation of action potential of the single motor unit occurs following depression of response by curare or decamethonium. Increased amplitude of unit potential results from partial resynchronization of subunit potential contributions which had been desynchronized by the differential effect of the blocking agent on subunit latency. Decline of unit potential subsequent to post-tetanic potentiation results from desynchronization of component contributions as had been observed with initial administration of blocking agent. The occurrence of these events in a single motor unit indicates that they take place at the nerve terminal or subterminal portion of the unit.

scholarly journals α2-Adrenergic Receptor and Isoflurane Modulation of Presynaptic Ca2+ Influx and Exocytosis in Hippocampal Neurons

2016 ◽  
Vol 125 (3) ◽  
pp. 535-546 ◽  
Author(s):  
Masato Hara ◽  
Zhen-Yu Zhou ◽  
Hugh C. Hemmings
Keyword(s):  
Action Potential ◽  
Neurotransmitter Release ◽  
Adrenergic Receptor ◽  
Presynaptic Inhibition ◽  
Hippocampal Neurons ◽  
Quantitative Imaging ◽  
Volatile Anesthetics ◽  
Fluorescent Biosensors ◽  
Selective Antagonist ◽  
Ca2 Channels

Abstract Background Evidence indicates that the anesthetic-sparing effects of α2-adrenergic receptor (AR) agonists involve α2A-AR heteroreceptors on nonadrenergic neurons. Since volatile anesthetics inhibit neurotransmitter release by reducing synaptic vesicle (SV) exocytosis, the authors hypothesized that α2-AR agonists inhibit nonadrenergic SV exocytosis and thereby potentiate presynaptic inhibition of exocytosis by isoflurane. Methods Quantitative imaging of fluorescent biosensors of action potential–evoked SV exocytosis (synaptophysin-pHluorin) and Ca2+ influx (GCaMP6) were used to characterize presynaptic actions of the clinically used α2-AR agonists dexmedetomidine and clonidine, and their interaction with isoflurane, in cultured rat hippocampal neurons. Results Dexmedetomidine (0.1 μM, n = 10) or clonidine (0.5 μM, n = 8) inhibited action potential–evoked exocytosis (54 ± 5% and 59 ± 8% of control, respectively; P < 0.001). Effects on exocytosis were blocked by the subtype-nonselective α2-AR antagonist atipamezole or the α2A-AR–selective antagonist BRL 44408 but not by the α2C-AR–selective antagonist JP 1302. Dexmedetomidine inhibited exocytosis and presynaptic Ca2+ influx without affecting Ca2+ coupling to exocytosis, consistent with an effect upstream of Ca2+–exocytosis coupling. Exocytosis coupled to both N-type and P/Q-type Ca2+ channels was inhibited by dexmedetomidine or clonidine. Dexmedetomidine potentiated inhibition of exocytosis by 0.7 mM isoflurane (to 42 ± 5%, compared to 63 ± 8% for isoflurane alone; P < 0.05). Conclusions Hippocampal SV exocytosis is inhibited by α2A-AR activation in proportion to reduced Ca2+ entry. These effects are additive with those of isoflurane, consistent with a role for α2A-AR presynaptic heteroreceptor inhibition of nonadrenergic synaptic transmission in the anesthetic-sparing effects of α2A-AR agonists.

scholarly journals S6 kinase localizes to the presynaptic active zone and functions with PDK1 to control synapse development

2011 ◽  
Vol 194 (6) ◽  
pp. 921-935 ◽  
Author(s):  
Ling Cheng ◽  
Cody Locke ◽  
Graeme W. Davis
Keyword(s):  
Active Zone ◽  
Neurotransmitter Release ◽  
Synaptic Function ◽  
Growth Factor Signaling ◽  
Neuron Type ◽  
S6 Kinase ◽  
Neuronal Dendrites ◽  
Presynaptic Boutons ◽  
Presynaptic Active Zone ◽  
Presynaptic Protein

The dimensions of neuronal dendrites, axons, and synaptic terminals are reproducibly specified for each neuron type, yet it remains unknown how these structures acquire their precise dimensions of length and diameter. Similarly, it remains unknown how active zone number and synaptic strength are specified relative the precise dimensions of presynaptic boutons. In this paper, we demonstrate that S6 kinase (S6K) localizes to the presynaptic active zone. Specifically, S6K colocalizes with the presynaptic protein Bruchpilot (Brp) and requires Brp for active zone localization. We then provide evidence that S6K functions downstream of presynaptic PDK1 to control synaptic bouton size, active zone number, and synaptic function without influencing presynaptic bouton number. We further demonstrate that PDK1 is also a presynaptic protein, though it is distributed more broadly. We present a model in which synaptic S6K responds to local extracellular nutrient and growth factor signaling at the synapse to modulate developmental size specification, including cell size, bouton size, active zone number, and neurotransmitter release.

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.

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