Inhibition by Volatile Anesthetics of Endogenous Glutamate Release from Synaptosomes by a Presynaptic Mechanism

1995 ◽  
Vol 82 (6) ◽  
pp. 1406-1416. ◽  
Author(s):  
Michael Schlame ◽  
Hugh C. Jr. Hemmings
Keyword(s):  
Neurotransmitter Release ◽  
Glutamate Release ◽  
Volatile Anesthetics ◽  
Nerve Terminals ◽  
General Anesthetics ◽  
Release Process ◽  
Excitatory Neurotransmitter ◽  
Vesicle Exocytosis ◽  
Presynaptic Nerve Terminals ◽  
Sites Of Action

Background Synaptic transmission is more sensitive than axonal conduction to the effects of general anesthetics. Previous studies of the synaptic effects of general anesthetics have focused on postsynaptic sites of action. We now provide direct biochemical evidence for a presynaptic effect of volatile anesthetics on neurotransmitter release. Methods Rat cerebrocortical synaptosomes (isolated presynaptic nerve terminals) were used to determine the effects of general anesthetics on the release of endogenous L-glutamate, the major fast excitatory neurotransmitter. Basal and evoked (by 4-aminopyridine, veratridine, increased KCl, or ionomycin) glutamate release were measured by continuous enzyme-coupled fluorometry. Results Clinical concentrations of volatile halogenated anesthetics, but not of pentobarbital, inhibited 4-aminopyridine-evoked Ca(2+)-dependent glutamate release. Halothane also inhibited veratridine-evoked glutamate release but not basal, KCl-evoked, or ionomycin-evoked glutamate release. Halothane inhibited both the 4-aminopyridine-evoked and the KCl-evoked increase in free intrasynaptosomal [Ca2+]. Conclusions Inhibition of glutamate release from presynaptic nerve terminals is a potential mechanism of volatile anesthetic action. Comparison of the sensitivity of glutamate release evoked by secretogogues that act at various steps in the neurotransmitter release process suggests that halothane does not affect Ca(2+)-secretion coupling or vesicle exocytosis but inhibits glutamate release at a step proximal to Ca2+ influx, perhaps by blocking presynaptic Na+ channels. Synaptosomal glutamate release evoked by 4-aminopyridine should provide a useful system for further characterization of the presynaptic effects of anesthetics.

scholarly journals Activation of Neurotransmitter Release in Hippocampal Nerve Terminals During Recovery From Intracellular Acidification

1999 ◽  
Vol 81 (6) ◽  
pp. 2627-2635 ◽  
Author(s):  
Louis-Eric Trudeau ◽  
Vladimir Parpura ◽  
Philip G. Haydon
Keyword(s):  
Intracellular Ph ◽  
Neurotransmitter Release ◽  
Hippocampal Neurons ◽  
Glutamate Release ◽  
Fold Increase ◽  
Nerve Terminals ◽  
Intracellular Acidification ◽  
Release Process ◽  
Mepsc Frequency ◽  
Recovery From Acidification

Activation of neurotransmitter release in hippocampal nerve terminals during recovery from intracellular acidification. Intracellular pH may be an important variable regulating neurotransmitter release. A number of pathological conditions, such as anoxia and ischemia, are known to influence intracellular pH, causing acidification of brain cells and excitotoxicity. We examined the effect of acidification on quantal glutamate release. Although acidification caused only modest changes in release, recovery from acidification was associated with a very large (60-fold) increase in the frequency of miniature excitatory postsynaptic currents (mEPSCs) in cultured hippocampal neurons. This was accompanied by a block of evoked EPSCs and a rise in intracellular free Ca2+([Ca2+]i). The rise in mEPSC frequency required extracellular Ca2+, but influx did not occur through voltage-operated channels. Because acidic pH is known to activate the Na+/H+ antiporter, we hypothesized that a resulting Na+ load could drive Ca2+influx through the Na+/Ca2+ exchanger during recovery from acidification. This hypothesis is supported by three observations. First, intracellular Na+ rises during acidification. Second, the elevation in [Ca2+]i and mEPSC frequency during recovery from acidification is prevented by the Na+/H+antiporter blocker EIPA applied during the acidification step. Third, the rise in free Ca2+ and mEPSC frequency is blocked by the Na+/Ca2+ exchanger blocker dimethylbenzamil. We thus propose that during recovery from intracellular acidification a massive activation of neurotransmitter release occurs because the successive activation of the Na+/H+ and Na+/Ca2+ exchangers in nerve terminals leads to an elevation of intracellular calcium. Our results suggest that changes in intracellular pH and especially recovery from acidification have extensive consequences for the release process in nerve terminals. Excessive release of glutamate through the proposed mechanism could be implicated in excitotoxic insults after anoxic or ischemic episodes.

Isoflurane Reduces Ischemia-induced Glutamate Release in Rats Subjected to Forebrain Ischemia

1995 ◽  
Vol 82 (4) ◽  
pp. 996-1003. ◽  
Author(s):  
Piyush M. Patel ◽  
John C. Drummond ◽  
Daniel J. Cole ◽  
Randall L. Goskowicz
Keyword(s):  
Parietal Cortex ◽  
Neurotransmitter Release ◽  
Minimum Alveolar Concentration ◽  
Mild Hypothermia ◽  
Dorsal Hippocampus ◽  
Glutamate Release ◽  
Control Group ◽  
Excitatory Neurotransmitter ◽  
Bilateral Carotid ◽  
Hypothermic Group

Background The release of excitatory neurotransmitters during ischemia is thought to contribute to ischemic neuronal injury. Volatile anesthetics have been shown to reduce excitatory neurotransmission in vitro, and it is conceivable that they reduce ischemia-induced neurotransmitter release. The current investigation was conducted to evaluate the effect of isoflurane and N2O-fentanyl anesthesia on ischemia-induced glutamate release in the rat and to compare it with that of mild hypothermia, an intervention known to reduce glutamate release significantly. Methods Microdialysis probes were implanted into the parietal cortex and dorsal hippocampus of four groups of anesthetized rats (n = 5 per group). The hypothermic group was anesthetized with 1.2% halothane. The two isoflurane groups were anesthetized with 0.5 minimum alveolar concentration or electroencephalographic burst-suppression doses of isoflurane (approximately 2 minimum alveolar concentration). The control group was anesthetized with 70% N2O-30% O2 and fentanyl. The pericranial temperature was maintained at 34 degrees C in the hypothermic group and at 38 degrees C in the remaining groups. Ischemia was induced by bilateral carotid artery occlusion with simultaneous hypotension to 35 mmHg for 10 min, followed by a reperfusion period of 70 min. Dialysate was collected before, during, and after ischemia. The concentrations of glutamate and glycine in the dialysate were measured by high-performance liquid chromatography. Results Preischemic glutamate and glycine concentrations in the dialysate were similar among the groups. Ischemia resulted in a significant increase in glutamate and glycine concentrations in the N2O-fentanyl groups in the parietal cortex and in the hippocampus. This increase in neurotransmitter concentrations did not occur in the hypothermic group in either structure. Isoflurane reduced glutamate concentrations in both structures and glycine concentrations in the hippocampus. In the parietal cortex, glycine concentrations did not increase in either isoflurane group. Conclusions Hypothermia inhibits ischemia-induced excitatory neurotransmitter release in the rat. Isoflurane, in comparison with a N2O-fentanyl-anesthetized state, significantly attenuates excitatory neurotransmitter release in the hippocampus. This effect of isoflurane is comparable to that of mild hypothermia.

Volatile Anesthetics Depress Glutamate Transmission Via Presynaptic Actions

1996 ◽  
Vol 85 (4) ◽  
pp. 823-834 ◽  
Author(s):  
Bruce M. MacIver ◽  
Anthony A. Mikulec ◽  
Shanti M. Amagasu ◽  
Frances A. Monroe
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Minimum Alveolar Concentration ◽  
Glutamate Release ◽  
Volatile Anesthetics ◽  
Excitatory Postsynaptic Potential ◽  
Dependent Manner ◽  
Paired Pulse ◽  
Paired Pulse Facilitation ◽  
Sites Of Action

Background Recent evidence for a presynaptic depression of glutamate release produced by volatile anesthetics prompted the current study of isoflurane and halothane effects on glutamate-mediated transmission in the mammalian central nervous system. Methods Electrophysiologic recordings from CA1 neurons in rat hippocampal brain slices were used to measure anesthetic effects on glutamate-mediated excitatory postsynaptic potential (EPSP) amplitudes and paired pulse facilitation. Paired pulse facilitation is known to be altered when the calcium-dependent release of glutamate is depressed, but not when EPSP amplitudes are depressed by postsynaptic mechanisms. Results Isoflurane depressed EPSP amplitudes over a concentration range of 0.35-2.8 vol %, with a 50% depression (EC50) occurring at 1.0 vol % (0.71 rat minimum alveolar concentration). This depression was accompanied by an increase in paired-pulse facilitation of approximately 30% at 1.7 vol %, using interpulse intervals of 120 ms. Halothane depressed EPSP amplitudes in a concentration-dependent manner (0.3-2.4 vol %, EC50 = 1.1 minimum alveolar concentration; 1.3 vol %) and also increased facilitation by approximately 20% at 1.2 vol %. These effects persisted in the presence of 10 microM bicuculline, indicating that enhanced gamma-aminobutyric acid-mediated inhibition was not involved. The anesthetic-induced increase in facilitation and EPSP depression was mimicked by lowering extracellular calcium, which is known to depress glutamate release at these synapses. The postsynaptic glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione depressed EPSP amplitudes with no change in facilitation. Conclusions Our results confirm earlier findings that clinically relevant concentrations of volatile anesthetics depress glutamate-mediated synaptic transmission. The observed increases in synaptic facilitation support recent findings from biochemical and electrophysiologic studies indicating presynaptic sites of action contribute to anesthetic-induced depression of excitatory transmission. This anesthetic-induced reduction in glutamate release would contribute to the central nervous system depression associated with anesthesia by adding to postsynaptic depressant actions on glutamate receptors.

Neuroprotective Role of the B Vitamins in the Modulation of the Central Glutamatergic Neurotransmission

2021 ◽  
Vol 20 ◽  
Author(s):  
Shu-Kuei Huang ◽  
Cheng-Wei Lu ◽  
Tzu-Yu Lin ◽  
Su-Jane Wang
Keyword(s):  
Glutamate Release ◽  
B Vitamins ◽  
Nerve Terminals ◽  
Normal Brain ◽  
Membrane Excitability ◽  
Presynaptic Nerve Terminal ◽  
Normal Brain Function ◽  
Vesicular Exocytosis ◽  
Presynaptic Nerve Terminals ◽  
Ca2 Channels

Background: Regulation of glutamate release is crucial for maintaining normal brain function, but excess glutamate release is implicated in many neuropathological conditions. Therefore, the minimum glutamate release from presynaptic nerve terminals is an important neuroprotective mechanism. Objective: In this mini-review, we analyze the three B vitamins, namely vitamin B2 (riboflavin), vitamin B6 (pyridoxine), and vitamin B12 (cyanocobalamin), that affect the 4-aminopyridine (4-AP)-evoked glutamate release from presynaptic nerve terminal in rat and discuss their neuroprotective role. Methods: In this study, the measurements include glutamate release, DiSC3(5), and Fura-2. Results: The riboflavin, pyridoxine, and cyanocobalamin produced significant inhibitory effects on 4-aminopyridine-evoked glutamate release from rat cerebrocortical nerve terminals (synaptosomes) in a dose-dependent relationship. These presynaptic inhibitory actions of glutamate release are attributed to inhibition of physiologic Ca2+-dependent vesicular exocytosis but not Ca2+-independent nonvesicular release. These effects also did not affect membrane excitability, while diminished cytosolic [Ca2+]c through a reduction of direct Ca2+ influx via Cav2.2 (N-type) and Cav2.1 (P/Q-type) Ca2+ channels, rather than through indirect Ca2+ induced Ca2+ release from ryanodine-sensitive intracellular stores. Furthermore, their effects were attenuated by GF109203X and Ro318220, two protein kinase C (PKC) inhibitors, suggesting suppression of PKC activity. Taken together, these results suggest that riboflavin, pyridoxine, and cyanocobalamin inhibit presynaptic vesicular glutamate release from rat cerebrocortical synaptosomes, through the depression Ca2+ influx via voltage-dependent Cav2.2 (N-type) and Cav2.1 (P/Q-type) Ca2+ channels, and PKC signaling cascade. Conclusion: Therefore, these B vitamins may reduce the strength of glutamatergic synaptic transmission and is of considerable importance as potential targets for therapeutic agents in glutamate-induced excitation-related diseases.

Determinants of the Sensitivity of AMPA Receptors to Xenon

2004 ◽  
Vol 100 (2) ◽  
pp. 347-358 ◽  
Author(s):  
Andrew J. R. Plested ◽  
Scott S. Wildman ◽  
William R. Lieb ◽  
Nicholas P. Franks
Keyword(s):  
Ampa Receptors ◽  
Glutamate Release ◽  
Single Point ◽  
Site Directed Mutagenesis ◽  
Single Point Mutation ◽  
General Anesthetics ◽  
High Concentration ◽  
Application System ◽  
Hek 293 ◽  
Excitatory Neurotransmitter

Background There is substantial and growing literature on the actions of general anesthetics on a variety of neurotransmitter-gated ion channels, with the greatest attention being focused on inhibitory gamma-amino butyric acid type A receptors. In contrast, glutamate receptors, the most important class of fast excitatory neurotransmitter-gated receptor channels, have received much less attention, and their role in the production of the anesthetic state remains controversial. Methods alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors formed from a variety of different subunits were expressed in Xenopus oocytes and HEK-293 cells, and their sensitivities to the inhalational general anesthetics xenon, isoflurane, and halothane were determined using two-electrode voltage clamp and patch clamp techniques. The effects of desensitization on anesthetic sensitivity were investigated using cyclothiazide and site-directed mutagenesis. An ultrarapid application system was also used to mimic rapid high-concentration glutamate release at synapses. Results The authors show that xenon can potently inhibit AMPA receptors when assayed using bath application of kainate. However, when the natural neurotransmitter l-glutamate is used under conditions in which the receptor desensitization is blocked and the peak of the glutamate-activated response can be accurately measured, the pattern of inhibition changes markedly. When desensitization is abolished by a single-point mutation (L497Y in GluR1 and the equivalent mutation L505Y in GluR4), the xenon inhibition is eliminated. When AMPA receptors are activated by glutamate using an ultrarapid application system that mimics synaptic conditions, sensitivity to xenon, halothane, and isoflurane is negligible. Conclusions AMPA receptors, when assayed in heterologous expression systems, showed a sensitivity to inhalational anesthetics that was minimal when glutamate was applied rapidly at high concentrations. Because these are the conditions that are most relevant to synaptic transmission, the authors conclude that AMPA receptors are unlikely to play a major role in the production of the anesthetic state by inhalational agents.

scholarly journals Resistance to Volatile Anesthetics by Mutations Enhancing Excitatory Neurotransmitter Release inCaenorhabditis elegans

Genetics ◽  
2004 ◽  
Vol 168 (2) ◽  
pp. 831-843 ◽  
Author(s):  
Ammar H. Hawasli ◽  
Owais Saifee ◽  
Christine Liu ◽  
Michael L. Nonet ◽  
C. Michael Crowder
Keyword(s):  
Neurotransmitter Release ◽  
Volatile Anesthetics ◽  
Excitatory Neurotransmitter

scholarly journals Isoflurane inhibits synaptic vesicle exocytosis through reduced Ca2+ influx, not Ca2+-exocytosis coupling

2015 ◽  
Vol 112 (38) ◽  
pp. 11959-11964 ◽  
Author(s):  
Joel P. Baumgart ◽  
Zhen-Yu Zhou ◽  
Masato Hara ◽  
Daniel C. Cook ◽  
Michael B. Hoppa ◽  
...  
Keyword(s):  
Synaptic Transmission ◽  
Synaptic Vesicle ◽  
Hippocampal Neurons ◽  
Volatile Anesthetic ◽  
Selective Inhibition ◽  
Nerve Terminals ◽  
General Anesthetics ◽  
Single Action ◽  
Presynaptic Mechanisms ◽  
Vesicle Exocytosis

Identifying presynaptic mechanisms of general anesthetics is critical to understanding their effects on synaptic transmission. We show that the volatile anesthetic isoflurane inhibits synaptic vesicle (SV) exocytosis at nerve terminals in dissociated rat hippocampal neurons through inhibition of presynaptic Ca2+ influx without significantly altering the Ca2+ sensitivity of SV exocytosis. A clinically relevant concentration of isoflurane (0.7 mM) inhibited changes in [Ca2+]i driven by single action potentials (APs) by 25 ± 3%, which in turn led to 62 ± 3% inhibition of single AP-triggered exocytosis at 4 mM extracellular Ca2+ ([Ca2+]e). Lowering external Ca2+ to match the isoflurane-induced reduction in Ca2+ entry led to an equivalent reduction in exocytosis. These data thus indicate that anesthetic inhibition of neurotransmitter release from small SVs occurs primarily through reduced axon terminal Ca2+ entry without significant direct effects on Ca2+-exocytosis coupling or on the SV fusion machinery. Isoflurane inhibition of exocytosis and Ca2+ influx was greater in glutamatergic compared with GABAergic nerve terminals, consistent with selective inhibition of excitatory synaptic transmission. Such alteration in the balance of excitatory to inhibitory transmission could mediate reduced neuronal interactions and network-selective effects observed in the anesthetized central nervous system.

scholarly journals Volatile anesthetics inhibit presynaptic cGMP signaling to depress presynaptic excitability in rat hippocampal neurons

2022 ◽  
Author(s):  
Iris A Speigel ◽  
Vanessa Osman ◽  
Hugh C Hemmings
Keyword(s):  
Hippocampal Neurons ◽  
Glutamate Release ◽  
Volatile Anesthetics ◽  
Guanosine Monophosphate ◽  
Hcn Channels ◽  
Presynaptic Function ◽  
Presynaptic Mechanisms ◽  
Cgmp Signaling ◽  
Vesicle Exocytosis

Volatile anesthetics alter presynaptic function including effects on Ca2+ influx and neurotransmitter release. These actions are proposed to play important roles in their pleiotropic neurophysiological effects including unconsciousness and amnesia. The nitric oxide and cyclic guanosine monophosphate (NO/cGMP) signaling pathway has been implicated in presynaptic mechanisms, and disruption of NO/cGMP signaling has been shown to alter sensitivity to volatile anesthetics in vivo. We investigated NO/cGMP signaling in relation to volatile anesthetic actions in cultured rat hippocampal neurons using pharmacological tools and genetically encoded biosensors of cGMP levels. Using the fluorescent biosensor cGull we found that electrical stmulation-evoked NMDA-type glutamate receptor-independent presynaptic cGMP transients were inhibited -33.2% by isoflurane (0.51 mM) and -23.8% by sevoflurane (0.57 mM) (p<0.0001) compared to a stimulation without anesthetic. Isoflurane and sevoflurane inhibition of stimulation-evoked increases in presynaptic Ca2+ concentration, measured with synaptophysin-GCaMP6f, and synaptic vesicle exocytosis, measured with synaptophysin-pHlourin, were reduced by in neurons expressing the cGMP scavenger sponGee. This reduction in anesthetic effect was recapitulated by inhibiting HCN channels, a cGMP-modulated effector that can facilitate glutamate release. We propose that volatile anesthetics depress presynaptic cGMP signaling and downstream effectors like HCN channels that are essential to presynaptic function and excitability. These findings identify a novel mechanism by which volatile anesthetics depress synaptic transmission via second messenger signaling involving the NO/cGMP pathway.

Volatile Anesthetics Bind Rat Synaptic Snare Proteins

2005 ◽  
Vol 103 (4) ◽  
pp. 768-778 ◽  
Author(s):  
Peter Nagele ◽  
J Brett Mendel ◽  
William J. Placzek ◽  
Barbara A. Scott ◽  
D André d'Avignon ◽  
...  
Keyword(s):  
Secondary Structure ◽  
Volatile Anesthetics ◽  
Snare Complex ◽  
Snare Proteins ◽  
General Anesthetics ◽  
Syntaxin 1A ◽  
Excitatory Neurotransmitter ◽  
Thrombin Cleavage ◽  
Resonance Relaxation ◽  
The Stability

Background Volatile general anesthetics (VAs) have a number of synaptic actions, one of which is to inhibit excitatory neurotransmitter release; however, no presynaptic VA binding proteins have been identified. Genetic data in Caenorhabditis elegans have led to the hypothesis that a protein that interacts with the presynaptic protein syntaxin 1A is a VA target. Motivated by this hypothesis, the authors measured the ability of syntaxin 1A and proteins that interact with syntaxin to bind to halothane and isoflurane. Methods Recombinant rat syntaxin 1A, SNAP-25B, VAMP2, and the ternary SNARE complex that they form were tested. Binding of VAs to these proteins was detected by F-nuclear magnetic resonance relaxation measurements. Structural alterations in the proteins were examined by circular dichroism and ability to form complexes. Results Volatile anesthetics did not bind to VAMP2. At concentrations in the clinical range, VAs did bind to SNAP-25B; however, binding was detected only in preparations containing SNAP-25B homomultimers. VAs also bound at clinical concentrations to both syntaxin and the SNARE complex. Addition of an N-terminal His6 tag to syntaxin abolished its ability to bind VAs despite normal secondary structure and ability to form SNARE complexes; thrombin cleavage of the tag restored VA binding. Thus, the VA binding site(s) has structural requirements and is not simply any alpha-helical bundle. VAs at supraclinical concentrations produced an increase in helicity of the SNARE complex; otherwise, VA binding produced no gross alteration in the stability or secondary structure of the SNARE complex. Conclusion SNARE proteins are potential synaptic targets of volatile anesthetics.

Sign in / Sign up

Export Citation Format

Share Document