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Denomme N, Hull JM, Mashour GA. Role of Voltage-Gated Sodium Channels in the Mechanism of Ether-Induced Unconsciousness. Pharmacol Rev 2019; 71:450-466. [PMID: 31471460 DOI: 10.1124/pr.118.016592] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Despite continuous clinical use for more than 170 years, the mechanism of general anesthetics has not been completely characterized. In this review, we focus on the role of voltage-gated sodium channels in the sedative-hypnotic actions of halogenated ethers, describing the history of anesthetic mechanisms research, the basic neurobiology and pharmacology of voltage-gated sodium channels, and the evidence for a mechanistic interaction between halogenated ethers and sodium channels in the induction of unconsciousness. We conclude with a more integrative perspective of how voltage-gated sodium channels might provide a critical link between molecular actions of the halogenated ethers and the more distributed network-level effects associated with the anesthetized state across species.
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Affiliation(s)
- Nicholas Denomme
- Departments of Pharmacology (N.D.) and Anesthesiology (G.A.M.), Center for Consciousness Science (N.D., G.A.M.), and Neuroscience Graduate Program (J.M.H., G.A.M.), University of Michigan, Ann Arbor, Michigan
| | - Jacob M Hull
- Departments of Pharmacology (N.D.) and Anesthesiology (G.A.M.), Center for Consciousness Science (N.D., G.A.M.), and Neuroscience Graduate Program (J.M.H., G.A.M.), University of Michigan, Ann Arbor, Michigan
| | - George A Mashour
- Departments of Pharmacology (N.D.) and Anesthesiology (G.A.M.), Center for Consciousness Science (N.D., G.A.M.), and Neuroscience Graduate Program (J.M.H., G.A.M.), University of Michigan, Ann Arbor, Michigan
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2
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Perouansky M, Hemmings HC. Bioblasts, anaesthesia, and power failure: rein in the excitement. Br J Anaesth 2018; 120:891-895. [PMID: 29661404 DOI: 10.1016/j.bja.2018.02.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Accepted: 02/19/2018] [Indexed: 11/30/2022] Open
Affiliation(s)
- M Perouansky
- Department of Anesthesiology, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA.
| | - H C Hemmings
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY, USA
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3
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Abstract
Abstract
Background
Previous studies showed that synaptic transmission is affected by general anesthetics, but an anesthetic dose response in freely moving animals has not been done. The hippocampus provides a neural network for the evaluation of isoflurane and pentobarbital on multisynaptic transmission that is relevant to memory function.
Methods
Male Long-Evans rats were implanted with multichannel and single electrodes in the hippocampus. Spontaneous local field potentials and evoked field potentials were recorded in freely behaving rats before (baseline) and after various doses of isoflurane (0.25 to 1.5%) and sodium pentobarbital (10 mg/kg intraperitoneal).
Results
Monosynaptic population excitatory postsynaptic potentials at the basal and apical dendrites of CA1 were significantly decreased at greater than or equal to 0.25% (n = 4) and greater than or equal to 1.0% (n = 6) isoflurane, respectively. The perforant path evoked multisynaptic response at CA1 was decreased by ~50% at greater than or equal to 0.25% isoflurane (n = 5). A decreased population excitatory postsynaptic potential was accompanied by increased paired-pulse facilitation. Population spike amplitude in relation to apical dendritic population excitatory postsynaptic potential was not significantly altered by isoflurane. Spontaneous hippocampal local field potential at 0.8 to 300 Hz was dose-dependently suppressed by isoflurane (n = 6), with local field potential power in the 50- to 150-Hz band showing the highest decrease with isoflurane dose, commensurate with the decrease in trisynaptic CA1 response. Low-dose pentobarbital (n = 7) administration decreased the perforant path evoked trisynaptic CA1 response and hippocampal local field potentials at 78 to 125 Hz.
Conclusions
Hippocampal networks are sensitive to low doses of isoflurane and pentobarbital, possibly through both glutamatergic and γ-aminobutyric acid–mediated transmission. Network disruption could help explain the impairment of hippocampal-dependent cognitive functions with low-dose anesthetic.
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4
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Ramírez MIG, Rodríguez-Arias LR, Santiago AO, Pizano AL, Zamora RL, Gregorio RV, Trenado C, Sánchez HMG, San-Juan D. Correlation Between Bispectral Index and Electrocorticographic Features During Epilepsy Surgery. Clin EEG Neurosci 2017; 48:272-279. [PMID: 27325591 DOI: 10.1177/1550059416654850] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Surgical resection guided by intraoperative electrocorticography (iECoG) has been in clinical use for many decades. The use of the bispectral index (BIS) for monitoring depth of anesthesia during different types of surgery, including epilepsy surgery, is increasing nowadays. The BIS is an EEG-derived variable indicating cortical electrical activity. However, the correlation between the BIS score and the iECoG score, with the purpose of optimizing the quality and time of the iECoG recordings in epilepsy surgery is unknown. The goal of this study was to evaluate the correlation between BIS values and iECoG parameters during the epilepsy surgery under anesthesia with propofol and fentanyl. This is a prospective study that included patients with epilepsy who underwent epilepsy surgery guided by BIS and iECoG (September 2008 to October 2013). Clinical, physiological, and sociodemographic characteristics are shown. We correlated the iECoG parameters (presence of burst suppressions [BS], suppression time [seconds], background frequency [Hz], and type of iECoG score by Mathern et al) with BIS values. We included 28 patients, 15/28 (53.5%) female, general mean age of 30.5 years (range 13-56 years). Patients underwent epilepsy surgery: 22/28 (79%) temporal and 6/28 (21%) extratemporal. We found a nonlinear polynomial cubic relationship between the mentioned variables noting that a BIS range of 40 to 60 gave the following results: iECoG BS periods <5 seconds, background frequency 10 to 17 Hz, and iECoG score 2 characterized by lack of >20-Hz background frequencies. No BS were observed with a BIS > 60. In conclusion BIS values and iECoG parameters during the epilepsy surgery under anesthesia with propofol and fentanyl have a nonlinear correlation. BS patterns were not found with a BIS > 60. These findings show that BIS is a nonlinear multidimensional measure, which possesses high variability with the iECoG parameters. BS patterns are not found with BIS > 60.
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Affiliation(s)
| | | | - Areli O Santiago
- 1 Neuroanesthesiology Department. National Institute of Neurology, Mexico City, Mexico
| | | | | | - Rafael V Gregorio
- 3 Clinical Neurophysiology Department, National Institute of Neurology, Mexico City, Mexico
| | - Carlos Trenado
- 4 Institute of Clinical Neuroscience and Medical Psychology, University Hospital Düsseldorf, Dusseldorf, Germany
| | - Héctor Manuel G Sánchez
- 5 Faculty of Medicine of the Autonomous University of Baja California, Campus of Mexicali, Mexicali, Baja California, Mexico
| | - Daniel San-Juan
- 3 Clinical Neurophysiology Department, National Institute of Neurology, Mexico City, Mexico
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5
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Zimin PI, Woods CB, Quintana A, Ramirez JM, Morgan PG, Sedensky MM. Glutamatergic Neurotransmission Links Sensitivity to Volatile Anesthetics with Mitochondrial Function. Curr Biol 2016; 26:2194-201. [PMID: 27498564 DOI: 10.1016/j.cub.2016.06.020] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 04/28/2016] [Accepted: 06/14/2016] [Indexed: 12/31/2022]
Abstract
An enigma of modern medicine has persisted for over 150 years. The mechanisms by which volatile anesthetics (VAs) produce their effects (loss of consciousness, analgesia, amnesia, and immobility) remain an unsolved mystery. Many attractive putative molecular targets have failed to produce a significant effect when genetically tested in whole-animal models [1-3]. However, mitochondrial defects increase VA sensitivity in diverse organisms from nematodes to humans [4-6]. Ndufs4 knockout (KO) mice lack a subunit of mitochondrial complex I and are strikingly hypersensitive to VAs yet resistant to the intravenous anesthetic ketamine [7]. The change in VA sensitivity is the largest reported for a mammal. Limiting NDUFS4 loss to a subset of glutamatergic neurons recapitulates the VA hypersensitivity of Ndufs4(KO) mice, while loss in GABAergic or cholinergic neurons does not. Baseline electrophysiologic function of CA1 pyramidal neurons does not differ between Ndufs4(KO) and control mice. Isoflurane concentrations that anesthetize only Ndufs4(KO) mice (0.6%) decreased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) only in Ndufs4(KO) CA1 neurons, while concentrations effective in control mice (1.2%) decreased sEPSC frequencies in both control and Ndufs4(KO) CA1 pyramidal cells. Spontaneous inhibitory postsynaptic currents (sIPSCs) were not differentially affected between genotypes. The effects of isoflurane were similar on evoked field excitatory postsynaptic potentials (fEPSPs) and paired pulse facilitation (PPF) in KO and control hippocampal slices. We propose that CA1 presynaptic excitatory neurotransmission is hypersensitive to isoflurane in Ndufs4(KO) mice due to the inhibition of pre-existing reduced complex I function, reaching a critical reduction that can no longer meet metabolic demands.
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Affiliation(s)
- Pavel I Zimin
- Center for Developmental Therapeutics, Seattle Children's Research Institute, Seattle, WA 98101, USA.
| | - Christian B Woods
- Center for Developmental Therapeutics, Seattle Children's Research Institute, Seattle, WA 98101, USA
| | - Albert Quintana
- Center for Developmental Therapeutics, Seattle Children's Research Institute, Seattle, WA 98101, USA; Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, WA 98101, USA
| | - Jan-Marino Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, WA 98101, USA
| | - Philip G Morgan
- Center for Developmental Therapeutics, Seattle Children's Research Institute, Seattle, WA 98101, USA
| | - Margaret M Sedensky
- Center for Developmental Therapeutics, Seattle Children's Research Institute, Seattle, WA 98101, USA
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Zalucki O, van Swinderen B. What is unconsciousness in a fly or a worm? A review of general anesthesia in different animal models. Conscious Cogn 2016; 44:72-88. [PMID: 27366985 DOI: 10.1016/j.concog.2016.06.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Revised: 05/31/2016] [Accepted: 06/20/2016] [Indexed: 12/14/2022]
Abstract
All animals are rendered unresponsive by general anesthetics. In humans, this is observed as a succession of endpoints from memory loss to unconsciousness to immobility. Across animals, anesthesia endpoints such as loss of responsiveness or immobility appear to require significantly different drug concentrations. A closer examination in key model organisms such as the mouse, fly, or the worm, uncovers a trend: more complex behaviors, either requiring several sub-behaviors, or multiple neural circuits working together, are more sensitive to volatile general anesthetics. This trend is also evident when measuring neural correlates of general anesthesia. Here, we review this complexity hypothesis in humans and model organisms, and attempt to reconcile these findings with the more recent view that general anesthetics potentiate endogenous sleep pathways in most animals. Finally, we propose a presynaptic mechanism, and thus an explanation for how these drugs might compromise a succession of brain functions of increasing complexity.
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Affiliation(s)
- Oressia Zalucki
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Bruno van Swinderen
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
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7
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Xie Z, McMillan K, Pike CM, Cahill AL, Herring BE, Wang Q, Fox AP. Interaction of anesthetics with neurotransmitter release machinery proteins. J Neurophysiol 2012; 109:758-67. [PMID: 23136341 DOI: 10.1152/jn.00666.2012] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
General anesthetics produce anesthesia by depressing central nervous system activity. Activation of inhibitory GABA(A) receptors plays a central role in the action of many clinically relevant general anesthetics. Even so, there is growing evidence that anesthetics can act at a presynaptic locus to inhibit neurotransmitter release. Our own data identified the neurotransmitter release machinery as a target for anesthetic action. In the present study, we sought to examine the site of anesthetic action more closely. Exocytosis was stimulated by directly elevating the intracellular Ca(2+) concentration at neurotransmitter release sites, thereby bypassing anesthetic effects on channels and receptors, allowing anesthetic effects on the neurotransmitter release machinery to be examined in isolation. Three different PC12 cell lines, which had the expression of different release machinery proteins stably suppressed by RNA interference, were used in these studies. Interestingly, there was still significant neurotransmitter release when these knockdown PC12 cells were stimulated. We have previously shown that etomidate, isoflurane, and propofol all inhibited the neurotransmitter release machinery in wild-type PC12 cells. In the present study, we show that knocking down synaptotagmin I completely prevented etomidate from inhibiting neurotransmitter release. Synaptotagmin I knockdown also diminished the inhibition produced by propofol and isoflurane, but the magnitude of the effect was not as large. Knockdown of SNAP-25 and SNAP-23 expression also changed the ability of these three anesthetics to inhibit neurotransmitter release. Our results suggest that general anesthetics inhibit the neurotransmitter release machinery by interacting with multiple SNARE and SNARE-associated proteins.
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Affiliation(s)
- Zheng Xie
- Department of Anesthesia and Critical Care, The University of Chicago, Chicago, IL 60637, USA.
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8
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Shin MC, Wakita M, Iwata S, Nonaka K, Kotani N, Akaike N. Comparative effects of pentobarbital on spontaneous and evoked transmitter release from inhibitory and excitatory nerve terminals in rat CA3 neurons. Brain Res Bull 2012; 90:10-8. [PMID: 23026118 DOI: 10.1016/j.brainresbull.2012.09.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Revised: 09/14/2012] [Accepted: 09/19/2012] [Indexed: 10/27/2022]
Abstract
Pentobarbital (PB) modulates GABA(A) receptor-mediated postsynaptic responses through various mechanisms, and can directly activate the channel at higher doses. These channels exist both pre- and postsynaptically, and on the soma outside the synapse. PB also inhibits voltage-dependent Na⁺ and Ca²⁺ channels to decrease excitatory synaptic transmission. Just how these different sites of action combine to contribute to the overall effects of PB on inhibitory and excitatory synaptic transmission is less clear. To compare these pre- and postsynaptic actions of PB, we used a 'synaptic bouton' preparation of isolated rat hippocampal CA3 pyramidal neurons where we could measure in single neurons the effects of PB on spontaneous and single bouton evoked GABAergic inhibitory and glutamatergic excitatory postsynaptic currents (sIPSCs, sEPSCs, eIPSCs and eEPSCs), respectively. Low (sedative) concentrations (3-10 μM) of PB increased the frequency and amplitude of sIPSCs and sEPSCs, and also presynaptically increased the amplitude of both eIPSCs and eEPSCs. There was no change in current kinetics at this low concentration. At higher concentrations (30-300 μM), PB decreased the frequency, and increased the amplitude of sIPSCs, and presynaptically decreased the amplitude of eIPSCs. The current decay phase of sIPSCs and eIPSCs was increased. An increase in both frequency and amplitude was seen for sEPSCs, while the eIPSCs was also decreased by a bicuculline-sensitive presynaptic effect. The results confirm the multiple sites of action of PB on inhibitory and excitatory transmission and demonstrate that the most sensitive site of action is on transmitter release, via effects on presynaptic GABA(A) receptors. At low concentrations, however, both glutamate and GABA release is similarly enhanced, making the final effects on neuronal excitability difficult to predict and dependent on the particular systems involved and/or on subtle differences in susceptibility amongst individuals. At higher concentrations, release of both transmitters is decreased, while the postsynaptic effects to increase IPSPs and decrease EPSCs would be expected to both results in reduced neuronal excitability.
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Affiliation(s)
- Min-Chul Shin
- Research Division for Life Sciences, Kumamoto Health Science University, Kumamoto 861-5598, Japan
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9
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Herold KF, Hemmings HC. Sodium channels as targets for volatile anesthetics. Front Pharmacol 2012; 3:50. [PMID: 22479247 PMCID: PMC3316150 DOI: 10.3389/fphar.2012.00050] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Accepted: 03/07/2012] [Indexed: 12/15/2022] Open
Abstract
The molecular mechanisms of modern inhaled anesthetics are still poorly understood although they are widely used in clinical settings. Considerable evidence supports effects on membrane proteins including ligand- and voltage-gated ion channels of excitable cells. Na+ channels are crucial to action potential initiation and propagation, and represent potential targets for volatile anesthetic effects on central nervous system depression. Inhibition of presynaptic Na+ channels leads to reduced neurotransmitter release at the synapse and could therefore contribute to the mechanisms by which volatile anesthetics produce their characteristic end points: amnesia, unconsciousness, and immobility. Early studies on crayfish and squid giant axon showed inhibition of Na+ currents by volatile anesthetics at high concentrations. Subsequent studies using native neuronal preparations and heterologous expression systems with various mammalian Na+ channel isoforms implicated inhibition of presynaptic Na+ channels in anesthetic actions at clinical concentrations. Volatile anesthetics reduce peak Na+ current (INa) and shift the voltage of half-maximal steady-state inactivation (h∞) toward more negative potentials, thus stabilizing the fast-inactivated state. Furthermore recovery from fast-inactivation is slowed, together with enhanced use-dependent block during pulse train protocols. These effects can depress presynaptic excitability, depolarization and Ca2+ entry, and ultimately reduce transmitter release. This reduction in transmitter release is more potent for glutamatergic compared to GABAergic terminals. Involvement of Na+ channel inhibition in mediating the immobility caused by volatile anesthetics has been demonstrated in animal studies, in which intrathecal infusion of the Na+ channel blocker tetrodotoxin increases volatile anesthetic potency, whereas infusion of the Na+ channels agonist veratridine reduces anesthetic potency. These studies indicate that inhibition of presynaptic Na+ channels by volatile anesthetics is involved in mediating some of their effects.
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Affiliation(s)
- Karl F Herold
- Department of Anesthesiology, Weill Cornell Medical College New York, NY, USA
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10
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Herring BE, Xie Z, Marks J, Fox AP. Isoflurane inhibits the neurotransmitter release machinery. J Neurophysiol 2009; 102:1265-73. [PMID: 19515956 DOI: 10.1152/jn.00252.2009] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Despite their importance, the mechanism of action of general anesthetics is still poorly understood. Facilitation of inhibitory GABA(A) receptors plays an important role in anesthesia, but other targets have also been linked to anesthetic actions. Anesthetics are known to suppress excitatory synaptic transmission, but it has been difficult to determine whether they act on the neurotransmitter release machinery itself. By directly elevating [Ca(2+)](i) at neurotransmitter release sites without altering plasma membrane channels or receptors, we show that the commonly used inhalational general anesthetic, isoflurane, inhibits neurotransmitter release at clinically relevant concentrations, in a dose-dependent fashion in PC12 cells and hippocampal neurons. We hypothesized that a SNARE and/or SNARE-associated protein represents an important target(s) for isoflurane. Overexpression of a syntaxin 1A mutant, previously shown in Caenorhabditis elegans to block the behavioral effects of isoflurane, completely eliminated the reduction in neurotransmitter release produced by isoflurane, without affecting release itself, thereby establishing the possibility that syntaxin 1A is an intermediary in isoflurane's ability to inhibit neurotransmitter release.
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Affiliation(s)
- Bruce E Herring
- Department of Neurobiology, Pharmacology and Physiology, University of Chicago, Chicago, Illinois 60637, USA
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Hemmings HC. Sodium channels and the synaptic mechanisms of inhaled anaesthetics. Br J Anaesth 2009; 103:61-9. [PMID: 19508978 DOI: 10.1093/bja/aep144] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
General anaesthetics act in an agent-specific manner on synaptic transmission in the central nervous system by enhancing inhibitory transmission and reducing excitatory transmission. The synaptic mechanisms of general anaesthetics involve both presynaptic effects on transmitter release and postsynaptic effects on receptor function. The halogenated volatile anaesthetics inhibit neuronal voltage-gated Na(+) channels at clinical concentrations. Reductions in neurotransmitter release by volatile anaesthetics involve inhibition of presynaptic action potentials as a result of Na(+) channel blockade. Although voltage-gated ion channels have been assumed to be insensitive to general anaesthetics, it is now evident that clinical concentrations of volatile anaesthetics inhibit Na(+) channels in isolated rat nerve terminals and neurons, as well as heterologously expressed mammalian Na(+) channel alpha subunits. Voltage-gated Na(+) channels have emerged as promising targets for some of the effects of the inhaled anaesthetics. Knowledge of the synaptic mechanisms of general anaesthetics is essential for optimization of anaesthetic techniques for advanced surgical procedures and for the development of improved anaesthetics.
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Affiliation(s)
- H C Hemmings
- Department of Anesthesiology, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10021, USA.
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Lukatch HS, Kiddoo CE, Maciver MB. Anesthetic-induced Burst Suppression EEG Activity Requires Glutamate-mediated Excitatory Synaptic Transmission. Cereb Cortex 2005; 15:1322-31. [PMID: 15647528 DOI: 10.1093/cercor/bhi015] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Many anesthetics evoke electroencephalogram (EEG) burst suppression activity in humans and animals during anesthesia, and the mechanisms underlying this activity remain unclear. The present study used a rat neocortical brain slice EEG preparation to investigate excitatory synaptic mechanisms underlying anesthetic-induced burst suppression activity. Excitatory synaptic mechanisms associated with burst suppression activity were probed using glutamate receptor antagonists (CNQX and APV), GABA receptor antagonists, and simultaneous whole cell patch clamp and microelectrode EEG recordings. Clinically relevant concentrations of thiopental (50--70 microM), propofol (5--10 microM) or isoflurane (0.7--2.1 vol%, 0.5--1.5 rat minimum aveolar concentration (MAC), 200--700 microM) evoked delta slow wave activity and burst suppression EEG patterns similar to in vivo responses. These effects on EEG signals were blocked by glutamate receptor antagonists CNQX (8.6 microM) or APV (50 microM). Depolarizing intracellular bursts (amplitude=34.7+/-4.5 mV; half width=132+/-60 ms) always accompanied EEG bursts, and hyperpolarization increased intracellular burst amplitudes. Barrages of glutamate-mediated excitatory events initiated EEG bursting activity. Glutamate-mediated excitatory postsynaptic currents were significantly depressed by higher anesthetic concentrations that depressed burst suppression EEG activity. A GABA(A) agonist produced a similar EEG effect to the anesthetics. It appears that anesthetic effects at both glutamate and GABA synapses contribute to EEG patterns seen during anesthesia.
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Affiliation(s)
- Heath S Lukatch
- Stanford Neuroscience Program and Neuropharmacology Laboratory, Stanford University School of Medicine, Stanford, CA 94305-5117, USA
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Multiple synaptic and membrane sites of anesthetic action in the CA1 region of rat hippocampal slices. BMC Neurosci 2004; 5:52. [PMID: 15579203 PMCID: PMC543467 DOI: 10.1186/1471-2202-5-52] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2004] [Accepted: 12/03/2004] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Anesthesia is produced by a depression of central nervous system function, however, the sites and mechanisms of action underlying this depression remain poorly defined. The present study compared and contrasted effects produced by five general anesthetics on synaptic circuitry in the CA1 region of hippocampal slices. RESULTS At clinically relevant and equi-effective concentrations, presynaptic and postsynaptic anesthetic actions were evident at glutamate-mediated excitatory synapses and at GABA-mediated inhibitory synapses. In addition, depressant effects on membrane excitability were observed for CA1 neuron discharge in response to direct current depolarization. Combined actions at several of these sites contributed to CA1 circuit depression, but the relative degree of effect at each site was different for each anesthetic studied. For example, most of propofol's depressant effect (> 70 %) was reversed with a GABA antagonist, but only a minor portion of isoflurane's depression was reversed (< 20 %). Differences were also apparent on glutamate synapses-pentobarbital depressed transmission by > 50 %, but thiopental by only < 25 %. CONCLUSIONS These results, in as much as they may be relevant to anesthesia, indicate that general anesthetics act at several discrete sites, supporting a multi-site, agent specific theory for anesthetic actions. No single effect site (e.g. GABA synapses) or mechanism of action (e.g. depressed membrane excitability) could account for all of the effects produced for any anesthetic studied.
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14
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Tenney JR, Duong TQ, King JA, Ludwig R, Ferris CF. Corticothalamic modulation during absence seizures in rats: a functional MRI assessment. Epilepsia 2003; 44:1133-40. [PMID: 12919383 PMCID: PMC2962948 DOI: 10.1046/j.1528-1157.2003.61002.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE Functional magnetic resonance imaging (fMRI) was used to identify areas of brain activation during absence seizures in an awake animal model. METHODS Blood-oxygenation-level-dependent (BOLD) fMRI in the brain was measured by using T2*-weighted echo planar imaging at 4.7 Tesla. BOLD imaging was performed before, during, and after absence seizure induction by using gamma-butyrolactone (GBL; 200 mg/kg, intraperitoneal). RESULTS The corticothalamic circuitry, critical for spike-wave discharge (SWD) formation in absence seizure, showed robust BOLD signal changes after GBL administration, consistent with EEG recordings in the same animals. Predominantly positive BOLD changes occurred in the thalamus. Sensory and parietal cortices showed mixed positive and negative BOLD changes, whereas temporal and motor cortices showed only negative BOLD changes. CONCLUSIONS With the BOLD fMRI technique, we demonstrated signal changes in brain areas that have been shown, with electrophysiology experiments, to be important for generating and maintaining the SWDs that characterize absence seizures. These results corroborate previous findings from lesion and electrophysiological experiments and show the technical feasibility of noninvasively imaging absence seizures in fully conscious rodents.
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Affiliation(s)
- Jeffrey R Tenney
- Center for Comparative Neuroimaging, Department of Psychiatry, University of Massachusetts Medical School Worcester, Massachusetts 01655, USA.
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15
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Altmann L, Welge P, Mensing T, Lilienthal H, Voss B, Wilhelm M. Chronic exposure to trichloroethylene affects neuronal plasticity in rat hippocampal slices. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2002; 12:157-167. [PMID: 21782635 DOI: 10.1016/s1382-6689(02)00032-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2001] [Revised: 04/16/2002] [Accepted: 05/02/2002] [Indexed: 05/31/2023]
Abstract
Inhalational exposure to organic solvents is known to exert neurotoxic effects. Using the new multielectrode dish system (Panasonic) the effects of chronic exposure to trichloroethylene (TCE) on neuronal plasticity were assessed in different regions of the adult rat brain. Two groups of Long-Evans rats were exposed to 0 ppm or 500 ppm TCE, respectively, 6 h/day, 5 days/week for 6 months. Long-term potentiation (LTP) as well as paired-pulse potentiation/inhibition were assessed in slices from the visual cortex and the hippocampus. In addition, several behavioral tests were performed. Trichloroethanol concentrations were measured in blood and trichloroacetic acid concentrations were determined in urine. While TCE exposure impaired LTP as well as paired-pulse potentiation in hippocampal slices, no effects were seen in cortical slices. Our data demonstrate brain region specific functional changes following TCE exposure with the hippocampus being more vulnerable than the visual cortex. The behavioral measurements revealed no TCE related effects.
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Affiliation(s)
- Lilo Altmann
- Medical Institute of Environmental Hygiene, Department of Neurobehavioral Toxicology, Auf'm Hennekamp 50, D-40225 Duesseldorf, FRG
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16
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Richards CD. Anaesthetic modulation of synaptic transmission in the mammalian CNS. Br J Anaesth 2002; 89:79-90. [PMID: 12173243 DOI: 10.1093/bja/aef162] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- C D Richards
- Department of Physiology, University College London, Gower Street, London WC1A 6BT, UK
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Ohta M, Saito T, Saito K, Kurasaki M, Hosokawa T. Effect of trichloroethylene on spatiotemporal pattern of LTP in mouse hippocampal slices. Int J Neurosci 2002; 111:257-71. [PMID: 11912680 DOI: 10.3109/00207450108994236] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The effect of trichloroethylene (TCE) on long-term potentiation (LTP) was studied using both electrical and optical recording. The hippocampi from mice injected with 300 mg/kg or 1000 mg/kg TCE were sliced 24 h after administration. The field potential from the CAI was recorded. After the application of tetanus, population spikes (PS) were potentiated in all groups, but the post-per-pre ratio of PS was smaller in TCE groups than in the control. Optical recording was also carried out in 1000 mg/kg TCE-injected mice and a new analytical method using a high speed camera was employed. After the induction of tetanus, the optical signal was potentiated in both TCE and control groups. However, the post-per-pre ratio of the optical signals and response area were smaller in the TCE groups than in the control. It was suggested that the impairment of LTP is one of the mechanisms of the impairment of immediate memory after acute exposure to TCE in humans.
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Affiliation(s)
- M Ohta
- Laboratory of Environmental Biology, Hokkaido University School of Medicine, Sapporo, Japan
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Frizelle HP, Moriarty DC, O'Connor JJ. Effects of the combination of halothane and serotonin uptake blockers on synaptic transmission in the rat dentate gyrus in vitro. J Basic Clin Physiol Pharmacol 2000; 11:29-45. [PMID: 10851661 DOI: 10.1515/jbcpp.2000.11.1.29] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Although the exact basis of their action remains unknown, volatile agents affect noradrenergic and serotoninergic systems. Imipramine and fluoxetine have documented effects on these neurotransmitter transmission systems. Given the common sites of action of these antidepressants and halothane, we examined their individual and combined effects on tonic excitatory post-synaptic potentials (EPSPs) and frequency dependent blockade in the rat dentate gyrus in vitro. Extracellular recordings of field EPSPs were maintained from the dentate gyrus, in the presence of picrotoxin (100 microM). Stimulation at 30 Hz (200 ms) allowed investigation of frequency dependent blockade. Once a stable equilibrium was established, halothane, imipramine and fluoxetine were administered via the perfusate and recordings were made. Halothane produced a dose dependent reduction in EPSP amplitude (EC50 0.28 mM; n = 12). Imipramine (1-10 microM) potentiated the EPSP amplitude (148.2 +/- 8.2%; imipramine 1 microM; n = 6). Fluoxetine (0.5-10 microM) reduced EPSP amplitude to 83.7 +/- 22.1% of control (n = 6). In the presence of halothane 0.2 mM, imipramine reduced the EPSP amplitude to 56.5 +/- 9.9% of control (imipramine 10 microM; n = 6; p < 0.05 compared with imipramine alone). Halothane (0.2 mM) demonstrated frequency dependent blockade. However, neither imipramine nor fluoxetine showed use dependent inhibition at the doses investigated. When combined with halothane 0.2 mM, fluoxetine 10 microM demonstrated frequency dependent blockade at the sixth pulse in the train compared with controls (13.8 +/- 4.7% vs 38.1 +/- 8.3%; n = 6; p < 0.05). The halothane-imipramine combination did not exhibit use dependent blockade greater than controls. The reversal of imipramine-induced EPSP potentiation by the preapplication of halothane has not been previously reported. It may be due to modulation of noradrenergic transmission by halothane. The frequency dependent blockade produced by the combination of fluoxetine 10 microM and halothane may be mediated by a nonspecific membrane effect on 5-HT uptake. These differing effects underline the broad action of volatile agents on synaptic mechanisms.
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Affiliation(s)
- H P Frizelle
- Department of Human Anatomy and Physiology, National University of Ireland, Dublin, Ireland
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Membrane and synaptic actions of halothane on rat hippocampal pyramidal neurons and inhibitory interneurons. J Neurosci 2000. [PMID: 10934238 DOI: 10.1523/jneurosci.20-16-05915.2000] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A relatively small number of inhibitory interneurons can control the excitability and synchronization of large numbers of pyramidal neurons in hippocampus and other cortical regions. Thus, anesthetic modulation of interneurons could play an important role during anesthesia. The aim of this study was to investigate effects of a general anesthetic, halothane, on membrane and synaptic properties of rat hippocampal interneurons. GABA receptor-mediated IPSCs were recorded with whole-cell patch-clamp techniques in visually identified CA1 pyramidal cells and interneurons located at the border of stratum lacunosum-moleculare and stratum radiatum. Halothane (0.35 mm congruent with 1.2 vol%) depressed evoked IPSC amplitudes recorded from both pyramidal cells and inhibitory interneurons. Also, halothane considerably prolonged the decay time constant of evoked IPSCs in pyramidal cells and interneurons. The frequencies of miniature IPSCs were increased by halothane (two- to threefold) in both types of neuron. On the other hand, halothane effects on resting membrane potentials were variable but minimal in both types of neurons. In current-clamp recordings, halothane depressed EPSP amplitudes and increased IPSP amplitudes recorded from both types of neurons. In addition, halothane increased the failure rate of synaptically evoked action potentials. Taken together, these data provide evidence that halothane increases GABA(A) receptor-mediated synaptic inhibition between synaptically connected interneurons and depresses excitatory transmission, similar to effects observed in pyramidal neurons.
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20
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Nishikawa K, MacIver MB. Membrane and synaptic actions of halothane on rat hippocampal pyramidal neurons and inhibitory interneurons. J Neurosci 2000; 20:5915-23. [PMID: 10934238 PMCID: PMC6772580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023] Open
Abstract
A relatively small number of inhibitory interneurons can control the excitability and synchronization of large numbers of pyramidal neurons in hippocampus and other cortical regions. Thus, anesthetic modulation of interneurons could play an important role during anesthesia. The aim of this study was to investigate effects of a general anesthetic, halothane, on membrane and synaptic properties of rat hippocampal interneurons. GABA receptor-mediated IPSCs were recorded with whole-cell patch-clamp techniques in visually identified CA1 pyramidal cells and interneurons located at the border of stratum lacunosum-moleculare and stratum radiatum. Halothane (0.35 mm congruent with 1.2 vol%) depressed evoked IPSC amplitudes recorded from both pyramidal cells and inhibitory interneurons. Also, halothane considerably prolonged the decay time constant of evoked IPSCs in pyramidal cells and interneurons. The frequencies of miniature IPSCs were increased by halothane (two- to threefold) in both types of neuron. On the other hand, halothane effects on resting membrane potentials were variable but minimal in both types of neurons. In current-clamp recordings, halothane depressed EPSP amplitudes and increased IPSP amplitudes recorded from both types of neurons. In addition, halothane increased the failure rate of synaptically evoked action potentials. Taken together, these data provide evidence that halothane increases GABA(A) receptor-mediated synaptic inhibition between synaptically connected interneurons and depresses excitatory transmission, similar to effects observed in pyramidal neurons.
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Affiliation(s)
- K Nishikawa
- Neuropharmacology Laboratory, Department of Anesthesia, Stanford University School of Medicine, Stanford, California 94305-5117, USA.
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Walker MC, Perry H, Scaravilli F, Patsalos PN, Shorvon SD, Jefferys JG. Halothane as a neuroprotectant during constant stimulation of the perforant path. Epilepsia 1999; 40:359-64. [PMID: 10080519 DOI: 10.1111/j.1528-1157.1999.tb00718.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
PURPOSE To determine the neuroprotective effects of halothane during constant stimulation of the perforant path. METHODS Male Sprague-Dawley rats had electrodes implanted into the perforant path and dentate granule cell layer under halothane anaesthesia (1-2% in oxygen). They were then divided into four groups. In group 1 (n = 9), the perforant path was stimulated at 20 Hz for 2 h under halothane anaesthesia (1-2%). In group 2 (n = 3), the animals were unstimulated but maintained under halothane anaesthesia (1-2%) for 2 h with the electrodes in place. Both groups 1 and 2 had the electrodes removed and were then allowed to recover fully from the anaesthetic. In groups 3 and 4, the electrodes were held in place with dental acrylic. Both of these groups were allowed to recover fully from anaesthesia. In group 3 (n = 3), 24-48 h after recovery from anaesthesia, the perforant path was stimulated at 20 Hz for 2 h. Group 4 (n = 3) received no stimulation. After 14-17 days, the rats were killed, and morphometry and cell counts were performed on the hippocampi from rats in groups 1 and 2. RESULTS Cell densities were not significantly different between control (group 2), unstimulated rats, and animals stimulated under halothane anaesthesia (group 1). Stimulation in the unanaesthetised rats resulted in severe neuronal loss in hilus, CA1, and CA3. CONCLUSIONS Halothane protects hippocampal neurons against damage induced by constant stimulation of the perforant path.
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Affiliation(s)
- M C Walker
- Epilepsy Research Group, University Department of Clinical Neurology, Institute of Neurology, Birmingham, England
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22
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Duch DS, Rehberg B, Vysotskaya TN. Volatile anesthetics significantly suppress central and peripheral mammalian sodium channels. Toxicol Lett 1998; 100-101:255-63. [PMID: 10049151 DOI: 10.1016/s0378-4274(98)00193-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
1. Voltage-dependent sodium channels are important for neuronal signal propagation and integration. 2. Non-mammalian preparations, such as squid giant axon, have sodium channels which have been found to be insensitive to clinical anesthetic concentrations. 3. On the other hand, sodium channels from mammalian neurons are much more sensitive to block by volatile anesthetics. 4. Due to a significant hyperpolarizing shift in steady-state inactivation, IC50s for sodium channel block at potentials close to the resting membrane potential overlapped with clinical anesthetic concentrations. 5. Hence, sodium channels in mammalian neurons may be sensitive molecular targets of volatile anesthetics.
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Affiliation(s)
- D S Duch
- Department of Anesthesiology, Cornell University Medical College, New York, NY 10021, USA
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23
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Larsen M, Langmoen IA. The effect of volatile anaesthetics on synaptic release and uptake of glutamate. Toxicol Lett 1998; 100-101:59-64. [PMID: 10049181 DOI: 10.1016/s0378-4274(98)00165-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
1. Volatile anaesthetics seem to exert their effects on several parts of the neuronal conducting system. 2. The effect on synaptic excitation seems to be quantitatively the most important (Berg-Johnsen and Langmoen, Acta Physiol. Scand. 128, 1986, 613-618) as 1 minimum alveolar concentration (MAC) of isoflurane reduces the activity in thin unmyelinated afferent fibres by 18%, excitatory synapses by 27% and postsynaptic neurones by 24%. 3. The reduction in excitatory synaptic transmission is caused by a decreased amount of transmitter glutamate in the synaptic cleft caused by a reduced release and increased uptake of glutamate in the presynaptic terminals (Larsen et al., Brain Res. 663, 1994, 335-337; Larsen et al., Br. J. Anaesth. 78, 1997, 55-59).
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Affiliation(s)
- M Larsen
- Institute for Surgical Research and Department of Neurosurgery, Rikshospitalet, National Hospital, Oslo, Norway.
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24
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Richards CD. What the actions of anaesthetics on fast synaptic transmission reveal about the molecular mechanism of anaesthesia. Toxicol Lett 1998; 100-101:41-50. [PMID: 10049173 DOI: 10.1016/s0378-4274(98)00163-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
1. Synapses with the brain are important components of the networks responsible for higher nervous function and current evidence suggests that general anaesthetics modulate synaptic transmission in the brain. 2. Analysis of anaesthetic action on these synapses not only defines the cellular mechanisms involved in anaesthesia but also reveals much about the molecular targets of anaesthetic action. 3. It appears that while anaesthetics affect a wide variety of processes, the most sensitive are those which are directly linked to the activity of ligand-gated ion channels. Moreover, both single channel patch clamp studies and the molecular biological investigations of the sub-unit specificity of the sensitivity to anaesthetics indicate that anaesthetics interact directly with these functional proteins.
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Affiliation(s)
- C D Richards
- Department of Physiology, Royal Free Hospital School of Medicine, London, UK.
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25
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Kirson ED, Yaari Y, Perouansky M. Presynaptic and postsynaptic actions of halothane at glutamatergic synapses in the mouse hippocampus. Br J Pharmacol 1998; 124:1607-14. [PMID: 9756375 PMCID: PMC1565559 DOI: 10.1038/sj.bjp.0701996] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Whole-cell patch-clamp recordings in adult mouse hippocampal slices were used to test the mechanism by which the volatile anesthetic halothane inhibits glutamate receptor-mediated synaptic transmission. Non-N-methyl-D-aspartate (nonNMDA) and NMDA receptor-mediated currents in CA1 pyramidal cells were pharmacologically isolated by bath application of D,L-2-amino-5-phosphonovaleric acid (APV; 100 microM) or 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX; 5 microM), respectively. Halothane blocked both nonNMDA and NMDA receptor-mediated excitatory postsynaptic currents (EPSCs) to a similar extent (IC50 values of 0.66 and 0.57 mM, respectively). Partial blockade of the EPSCs by lowering the extracellular concentration of calcium ([Ca2+]o), but not by application of CNQX (1 microM), was accompanied by an increase in paired-pulse facilitation (PPF). Halothane-induced blockade of the EPSCs also was associated with an increase in PPF. The effects of halothane on alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and NMDA receptor-mediated currents induced by agonist iontophoresis, were compared. AMPA-induced currents were blocked with an IC50 of 1.7 mM. NMDA-induced currents were significantly less sensitive to halothane (IC50 of 5.9 mM). The effect of halothane on iontophoretic AMPA dose-response curves was tested. Halothane suppressed the maximal response to AMPA without affecting its EC50, suggesting a noncompetitive mechanism of inhibition. All effects of halothane were reversible upon termination of the exposure to the drug. These data suggest that halothane blocks central glutamatergic synaptic transmission by presynaptically inhibiting glutamate release and postsynaptically blocking the AMPA subtype of glutamate receptors.
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Affiliation(s)
- E D Kirson
- Department of Physiology, Hebrew University-Hadassah School of Medicine, Jerusalem, Israel
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26
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Ouanounou A, Carlen PL, El-Beheiry H. Enhanced isoflurane suppression of excitatory synaptic transmission in the aged rat hippocampus. Br J Pharmacol 1998; 124:1075-82. [PMID: 9720776 PMCID: PMC1565481 DOI: 10.1038/sj.bjp.0701911] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The effects of the volatile anaesthetic, isoflurane, were investigated on evoked dendritic field excitatory postsynaptic potentials (f.e.p.s.p.) and antidromic and orthodromic population spikes recorded extracellularly in the CA1 cell layer region in the in vitro hippocampal slice taken from young mature (2-3 months) and old (24-27 months) Fisher 344 rats. 2. Isoflurane depressed the f.e.p.s.ps and the orthodromically-evoked population spikes in both old and young hippocampi. However, the magnitude of the anaesthetic-induced depression was greater in slices taken from old rats compared to those taken from young rats during the application of different isoflurane concentrations (0.5-5%). 3. In the presence of the GABA(A) antagonist, bicuculline methiodide (15 microM), isoflurane suppressed the f.e.p.s.ps to the same extent as was observed in the absence of the GABA(A) antagonist. 4. Orthodromically evoked population spikes were suppressed by isoflurane in a manner quantitatively similar to the suppression of the f.e.p.s.ps. However, antidromic population spikes and presynaptic volleys evoked in young and old slices were resistant to anaesthetic action. In addition, paired pulse facilitation ratio of the evoked dendritic f.e.p.s.ps was not affected in both young and old slices during the application of isoflurane. 5. When slices were exposed to low Ca2+/high Mg2+ solution, isoflurane (1 and 3%) depressed the f.e.p.s.ps in aged slices to the same extent as in young slices. 6. The augmented anaesthetic depression of f.e.p.s.ps in old compared to young hippocampi in the absence and presence of bicuculline, and the lack of anaesthetic effects on antidromic population spikes and presynaptic volleys in old and young slices, suggest that the increased sensitivity of anaesthetic actions in old hippocampi is due to age-induced attenuation of synaptic excitation rather than potentiation of synaptic inhibition. Furthermore, elimination of the increased sensitivity of old slices to anaesthetic actions when the slices were perfused with low Ca2+/high Mg2+ medium, which presumably would decrease intracellular [Ca2+], suggests that the enhanced anaesthetic effects in aged neurones might be related to increased intraneuronal [Ca2+] in the synaptic terminal.
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Affiliation(s)
- A Ouanounou
- Department of Medicine (Neurology), University of Toronto, The Toronto Hospital, Western Division, Ontario, Canada
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27
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Nikonorov IM, Blanck TJ, Recio-Pinto E. The effects of halothane on single human neuronal L-type calcium channels. Anesth Analg 1998; 86:885-95. [PMID: 9539620 DOI: 10.1097/00000539-199804000-00038] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
UNLABELLED We investigated halothane's effects on the function of L-type Ca2+ channels in a human neuronal cell line, SH-SY5Y, by using the cell-attached patch voltage clamp configuration and Ba2+ as the charge carrier. In multiple-channel patches, halothane decreased the peak and persistent Ba2+ currents, accelerated the rate of inactivation, and slowed the rate of activation. Single-channel analysis showed that halothane (0.14-1.26 mM) increased the latency time for the first channel opening, increased the lifetime of nonconducting events, increased the proportion of short-lived open events, decreased the lifetime of the two open populations, and increased the percentage of current traces without channel activity. All of the observed halothane effects contribute to the halothane-induced decrease in macroscopic Ba2+ currents. The halothane concentration producing 50% reduction (IC50) of the peak Ba2+ current was 0.80 mM (approximately 1.9 hypothetical minimum alveolar anesthetic concentration [H-MAC] at 28 degrees C) and of the persistent Ba2+ current was 0.69 mM (approximately 1.7 H-MAC). The halothane effects did not always occur together, and the Hill slope of 1.6 suggested the presence of more than one interaction site or of more than one population of L-type Ca2+ channels. Halothane reduces L-type Ca2+ channel currents in human neuronal cells primarily through the stabilization of nonconducting states such as closed (before and after channel opening) and inactivated states. IMPLICATIONS Calcium is a signaling molecule in neurons. We measured the effect of halothane on Ba2+ (a Ca2+ surrogate) movement into a human neuron-like cell electronically. Ba2+ entry through the L-type channel was depressed. Halothane decreased the likelihood of the channel opening and enhanced the rate at which the channel closed and inactivated. These actions of halothane are probably related to its anesthetic action.
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Affiliation(s)
- I M Nikonorov
- Department of Anesthesiology, The Hospital for Special Surgery, New York, New York 10021, USA
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28
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Nikonorov IM, Blanck TJJ, Recio-Pinto E. The Effects of Halothane on Single Human Neuronal L-Type Calcium Channels. Anesth Analg 1998. [DOI: 10.1213/00000539-199804000-00038] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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29
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Larsen M, Valo E, Berg-Johnsen J, Langmoen I. Isoflurane reduces synaptic glutamate release without changing cytosolic free calcium in isolated nerve terminals. Eur J Anaesthesiol 1998. [DOI: 10.1111/j.0265-0215.1998.00275.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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30
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Felisberti F, Antkowiak B, Kirschfeld K. Effects of volatile anaesthetics on the membrane potential and ion channels of cultured neocortical astrocytes. Brain Res 1997; 766:56-65. [PMID: 9359587 DOI: 10.1016/s0006-8993(97)00554-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Volatile anaesthetics cause changes in the membrane resting potential of central neurons. This effect probably arises from actions on neuronal ion channels, but may also involve alterations in the ion composition of the extracellular space. Since glial cells play a key role in regulating the extracellular ion composition in the brains of mammals, we analyzed the effects of halothane, isoflurane and enflurane on the membrane conductances and ion channels of cultured cortical astrocytes. Astrocytes were dissociated from the neocortex of 0-2-day old rats and grown in culture for 3-4 weeks. Anaesthetic-induced changes in the membrane potential were recorded in the whole cell current-clamp configuration of the patch-clamp technique. We further studied the effects of halothane and enflurane on single ion channels in excised membrane patches. At concentrations corresponding to 1-2 MAC (1 MAC induces general anaesthesia in 50% of the patients and rats), membrane potentials recorded in the presence of enflurane, isoflurane and halothane did not differ significantly from the control values. At higher concentrations, effects of enflurane and halothane, but not of isoflurane, were statistically significant. Single-channel recordings revealed that halothane and enflurane activated a high conductance anion channel, which possibly mediated the effects observed during whole cell recordings. In less than 10% of the membrane patches, volatile anaesthetics either increased or decreased the mean open time of K+-selective ion channels without altering single-channel conductances. In summary, it seems unlikely that the actions of volatile anaesthetics described here are involved in the state of general anaesthesia. Statistically significant effects occurred at concentrations ten times higher than those required to cause half-maximal depression of action potential firing of neocortical neurons in cultured brain slices. However, it cannot be excluded that the changes observed in the membrane conductance of cortical astrocytes disturb the physiological function of these cells, thereby influencing the membrane resting potential of neurons.
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Affiliation(s)
- F Felisberti
- Psychology Department, University Park Nottingham, UK
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31
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Hirota K, Roth SH. The effects of sevoflurane on population spikes in CA1 and dentate gyrus of the rat hippocampus in vitro. Anesth Analg 1997; 85:426-30. [PMID: 9249125 DOI: 10.1097/00000539-199708000-00032] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
UNLABELLED We studied the effects of sevoflurane on population spikes (PSs) in two synaptic pathways in rat hippocampal slices. Stimulating electrodes were placed on Schaffer collateral fibers or perforant path to activate inputs to CA1 pyramidal neurons or dentate gyrus (DG) neurons, respectively. Extracellular glass microelectrodes were used to record PSs. The paired-pulse stimulus was used to induce the paired-pulse facilitation (PPF). Sevoflurane (0.4-5.0 vol%) significantly decreased the amplitudes of PSs of CA1 and DG in a dose-dependent and reversible manner (25% effective dose values were 4.1 and 0.9 vol%, respectively). The stimulus-response relationships for PS amplitudes revealed that sevoflurane increased the threshold for PS generation in CA1 and DG. Sevoflurane (2.0 vol%) significantly enhanced PPF from 127% and 263% to 153% and 494% in CA1 and DG, respectively. The results imply that the effects of sevoflurane on PSs are greater in DG than in CA1 neurons, that sevoflurane enhances the PPF in both CA1 and DG, and that the actions of sevoflurane are not similar to those of other volatile or intravenous anesthetics previously reported in hippocampal preparations. IMPLICATIONS The volatile anesthetic sevoflurane alters neural excitability of individual pathways in the hippocampus in a manner different from other general anesthetics. The results are consistent with a site-specific mechanism of action for general anesthesia.
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Affiliation(s)
- K Hirota
- Department of Anesthesiology, Toyama Medical and Pharmaceutical University School of Medicine, Sugitani, Japan
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32
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Hirota K, Roth SH. The Effects of Sevoflurane on Population Spikes in CA1 and Dentate Gyrus of the Rat Hippocampus In Vitro. Anesth Analg 1997. [DOI: 10.1213/00000539-199708000-00032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Antkowiak B, Heck D. Effects of the volatile anesthetic enflurane on spontaneous discharge rate and GABA(A)-mediated inhibition of Purkinje cells in rat cerebellar slices. J Neurophysiol 1997; 77:2525-38. [PMID: 9163374 DOI: 10.1152/jn.1997.77.5.2525] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The effects of the volatile anesthetic enflurane on the spontaneous action potential firing and on gamma-aminobutyric acid-A (GABA(A))-mediated synaptic inhibition of Purkinje cells were investigated in sagittal cerebellar slices. The anesthetic shifted the discharge patterns from continuous spiking toward burst firing and decreased the frequency of extracellularly recorded spontaneous action potentials in a concentration-dependent manner. Half-maximal reduction was observed at a concentration corresponding to 2 MAC (1 MAC induces general anesthesia in 50% of patients and rats). When the GABA(A) antagonist bicuculline was present, 2 MAC enflurane reduced action potential firing only by 13 +/- 8% (mean +/- SE). In further experiments, inhibitory postsynaptic currents (IPSCs) were monitored in the whole cell patch-clamp configuration from cells voltage clamped close to -80 mV. At 1 MAC, enflurane attenuated the mean amplitude of IPSCs by 54 +/- 3% while simultaneously prolonging the time courses of monoexponential current decays by 413 +/- 69%. These effects were similar when presynaptic action potentials were suppressed by 1 microM tetrodotoxin. At 1-2 MAC, enflurane increased GABA(A)-mediated inhibition of Purkinje cells by 97 +/- 20% to 159 +/- 38%. During current-clamp recordings, the anesthetic (2 MAC) hyperpolarized the membrane potential by 5.2 +/- 1.1 mV in the absence, but only by 1.6 +/- 1.2 mV in the presence, of bicuculline. These results suggest that enflurane-induced membrane hyperpolarizations, as well as the reduction of spike rates, were partly caused by an increase in synaptic inhibition. Induction of burst firing was related to other actions of the anesthetic, probably an accelerated activation of an inwardly directed cationic current and a depression of spike afterhyperpolarizations.
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Affiliation(s)
- B Antkowiak
- Max-Planck-Institut für Biologische Kybernetik, Tuebingen, Germany
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Minami K, Yanagihara N, Segawa K, Tsutsui M, Shigematsu A, Izumi F. Inhibitory effects of propofol on catecholamine secretion and uptake in cultured bovine adrenal medullary cells. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1996; 353:572-8. [PMID: 8740152 DOI: 10.1007/bf00169178] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
In the central and peripheral noradrenergic neurons, the balance between noradrenaline release and reuptake determines the level of noradrenaline at the synaptic cleft or the nerve ending. In the present study, we examined the effects of propofol, an intravenous general anaesthetic, on catecholamine secretion and noradrenaline uptake in cultured bovine adrenal medullary cells and on the serum noradrenaline and blood pressure in rats. In cultured adrenal medullary cells, propofol (10-50 mumol/l) concentration-dependently inhibited catecholamine secretion stimulated by carbachol. Propofol suppressed carbachol-evoked 22Na+ influx as well as 45Ca2+ influx at concentrations similar to those which suppressed the catecholamine secretion. Propofol (10-50 mumol/l) also inhibited veratridine-evoked 22Na+ influx, 45Ca2+ influx and catecholamine secretion, whereas it had little effect on the 45Ca2+ influx and catecholamine secretion induced by 56 mmol/l K+. Cultured adrenal medullary cells show [3H] noradrenaline uptake which is sensitive to imipramine. Propofol (10-50 mumol/l) significantly inhibited the imipramine-sensitive uptake of [3H] noradrenaline. In rats, intravenous administration of propofol (2.5 mg/kg) lowered serum noradrenaline and arterial blood pressure. From these findings, in spite of inhibiting noradrenaline uptake, propofol at anaesthetic concentrations (10-30 mumol/l) seems to reduce catecholamine secretion by interfering with Na+ influx through voltage-dependent Na+ channels as well as nicotinic acetylcholine receptor-associated ion channels in the adrenal medulla and, probably, in the sympathetic nervous system. This may explain the propofol-induced hypotension during anaesthesia.
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Affiliation(s)
- K Minami
- Department of Anaesthesiology, University of Occupational and Environmental Health, School of Medicine, Kitakyushu, Japan
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35
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Narimatsu E, Tsai YC, Gerhold TD, Kamath SH, Davies LR, Sokoll MD. A Comparison of the Effect of Halothane on N-Methyl-D-Aspartate and Non-N-Methyl-D-Aspartate Receptor-Mediated Excitatory Synaptic Transmission in the Hippocampus. Anesth Analg 1996. [DOI: 10.1213/00000539-199604000-00029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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36
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Narimatsu E, Tsai YC, Gerhold TD, Kamath SH, Davies LR, Sokoll MD. A comparison of the effect of halothane on N-methyl-D-aspartate and non-N-methyl-D-aspartate receptor-mediated excitatory synaptic transmission in the hippocampus. Anesth Analg 1996; 82:843-7. [PMID: 8615508 DOI: 10.1097/00000539-199604000-00029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Halothane depresses synaptic transmission in the rat brain. First we determined the concentration of halothane which decreased the amplitude of the population spike recorded in the CA1 region of the hippocampus to 50% of the control value (105 +/- 4.9 micrograms/mL [0.53 mM] halothane). Hippocampal glutamate receptors are divided into N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionate (AMPA) and kainate (non-NMDA) subtypes. The NMDA and non-NMDA receptors were blocked with (+/-)-2-amino-5-phosphonopentanoic acid (AP5) (30 microM), and 6,7-dinitroquinoxaline-2,3-dione (DNQX) (10 microM), respectively, to allow observation of the effects of halothane on the NMDA and non-NMDA receptors, respectively. gamma-Aminobutyric acid type A (GABAA) receptors were blocked in all studies with picrotoxin (PTX) (40 microM). When the non-NMDA receptors were blocked a halothane concentration of 38.1 +/- 5.6 mg/mL was required to produce a further 50% decrease in population spike amplitude. When NMDA receptors were blocked with AP5 or only GABAA receptors were blocked the halothane concentrations needed to produce 50% block were higher than needed for the control (160.8 +/- 17.8 and 190.2 +/- 12.1 microgram/mL, respectively). These studies indicate that the NMDA receptors are more sensitive to the effects of halothane than the non-NMDA receptors.
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Affiliation(s)
- E Narimatsu
- Department of Anesthesia, University of Iowa, College of Medicine, Iowa City 52242, USA
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37
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Little HJ. How has molecular pharmacology contributed to our understanding of the mechanism(s) of general anesthesia? Pharmacol Ther 1996; 69:37-58. [PMID: 8857302 DOI: 10.1016/0163-7258(95)02030-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
This review discusses the mechanism(s) of general anesthesia from a pharmacological viewpoint; in particular, the ability of drugs to produce many different effects is emphasised. The problems of experimental measurement of general anesthesia are discussed, and the possibilities for antagonism and potentiation of anesthesia considered. Physicochemical studies on anesthesia are described, as are the advancement of ideas beyond consideration of lipids and proteins as separate sites of action. The importance of studies on different areas of the brain is highlighted, and the review finishes with a survey of the effects of general anesthetics on synaptic transmission which emphasises the problems of extrapolation from in vitro to in vivo.
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Affiliation(s)
- H J Little
- Department of Psychology, Durham University, UK
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38
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Yamamori Y, Kishikawa K, Collins JG. Halothane effects on low-threshold receptive field size of rat spinal dorsal horn neurons appear to be independent of supraspinal modulatory systems. Brain Res 1995; 702:162-8. [PMID: 8846071 DOI: 10.1016/0006-8993(95)01037-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Recent evidence strongly supports the importance of spinal sites of action for the ability of general anesthetic agents to block response to noxious stimuli. This study was designed to examine possible spinal anesthetic effects on non-noxiously evoked activity. Three groups of rats were prepared for acute experiments in which the response of spinal dorsal horn neurons to low threshold receptive field (RF) stimulation was evaluated. In each animal in each group extracellular activity was recorded from a single spinal dorsal horn neuron. A low-threshold RF of each neuron and, at times, the sensitivity to low-threshold stimulation of multiple sites in the RF were determined under baseline conditions (light anesthesia or decerebrate). In Group 1, reversible cooling of the thoracic spinal cord in the presence of either 0.5% or 1% halothane anesthesia caused no change in RF size. However, an increase from 0.5% to 1% halothane caused a 53% decrease in RF size both in the presence and absence of a reversible cold block of the spinal cord. In Group 2, animals with spinal cords transected at the thoracic level had a similar change in low-threshold receptive field size (52%) when halothane concentrations were increased from 0.5% to 1%. Testing sensitivity within the RF areas indicated that the silenced areas at the fringe of the receptive field could still elicit activation of spinal dorsal horn neurons but at a higher threshold. In the final group of animals, decerebration and spinal cord transection allowed us to compare effects of 0.5% and 1% halothane with an anesthetic free baseline. Here, again, a dose-dependent reduction in RF area was observed although the baseline RFs were significantly smaller than those in Groups 1 and 2. These results demonstrate that the reduction in low-threshold receptive field size due to the administration of the inhalation anesthetic halothane occurs in the absence of descending modulation from supraspinal sites. This implicates the spinal dorsal horn as a potentially important site of action for general anesthetics. These results also support the spinal cord as an important tool to study the pharmacology responsible for anesthetic effects on sensory processing.
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Affiliation(s)
- Y Yamamori
- Department of Anesthesiology, Yale University School of Medicine, New Haven, CT 06510, USA
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Kawabata K, Sumikawa K, Kamibayashi T, Fukumitsu K, Hayashi Y, Takada K, Yoshiya I. Effect of local anaesthetics on the stimulus-secretion coupling in bovine adrenal chromaffin cells. J Pharm Pharmacol 1993; 45:632-5. [PMID: 8105059 DOI: 10.1111/j.2042-7158.1993.tb05667.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
This study was carried out to determine the relative potencies of local anesthetics to inhibit the cholinergic synaptic transmission using cultured bovine adrenal chromaffin cells, and to clarify if the inhibitory action would correlate with biophysical and pharmacological properties. Local anaesthetics (bupivacaine, etidocaine, tetracaine, lignocaine and procaine; 0.02-2 mM) inhibited carbachol-induced catecholamine release from the cells in a concentration-dependent manner. This inhibition was completely reversible. IC50 (concentration of 50% inhibition) of each anaesthetic showed no correlation with the lipid solubility. The local anaesthetics showed greater inhibitory potency at a higher extracellular pH. The results suggest that clinically relevant concentrations of local anaesthetics inhibit the stimulus-secretion coupling in the chromaffin cells. The un-ionized based form plays a major role, and the inhibitory potency does not depend on the lipid solubility of the anaesthetics.
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Affiliation(s)
- K Kawabata
- Department of Anesthesiology, Osaka University Medial School, Japan
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40
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Abstract
1. This paper briefly reviews mechanisms by which such widely-used volatile anaesthetics as halothane and isoflurane suppress neural function in the brain. 2. In general, anaesthetics tend to depress neuronal firing and excitatory synaptic transmission, and potentiate synaptic inhibition. 3. According to recent evidence, a particular important action of anaesthetics is to inactivate a variety of both voltage-dependent and agonist-triggered Ca-currents. 4. Activation of K outward currents and Na inward currents probably occurs only with higher doses of anaesthetics. 5. How anaesthetics interfere with Ca-channels remains largely a matter of speculation--though some evidence favours a Ca-mediated action, following Ca2+ release from internal stores, that may account also for potentiation of IPSPs by prolonging the opening of GABA-activated Cl- channels. 6. Whatever its precise underlying mechanism, a suppression of Ca-influx into pre-synaptic terminals could well account for the depression of excitatory synaptic transmission.
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Affiliation(s)
- K Krnjević
- Anaesthesia Research Department, McGill University, Montreal, Québec, Canada
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41
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Langmoen IA, Hegstad E, Berg-Johnsen J. An experimental study of the effect of isoflurane on epileptiform bursts. Epilepsy Res 1992; 11:153-7. [PMID: 1396529 DOI: 10.1016/0920-1211(92)90093-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The effect of isoflurane on penicillin- and picrotoxin-induced epileptiform activity was tested using hippocampal slice preparations. Isoflurane reduced both the frequency of spontaneous epileptiform bursts and the number of population spikes within each burst in a dose-dependent manner. The last population spikes in the burst were most sensitive to the anesthetic, whereas the first 4-6 spikes were quite resistant and persisted until spontaneous activity was abolished at 3% isoflurane. Isoflurane increased the stimulus current required to evoke epileptiform bursts and shifted the relationship between stimulus current and population spike amplitude to the right. At 3% isoflurane, a dose that usually causes iso-electric EEG and abolishes all spontaneous epileptiform activity, responses could still be evoked, and then invariably had an epileptiform pattern. The maximum response was reduced compared to control and 1.5% isoflurane. With isoflurane there was a reduced tendency for activity to be transmitted from one region within the hippocampus to the other. This effect was also dose-dependent. However, transmitted activity always retained a typical epileptiform character, although the number of population spikes within a train to some extent decreased with increasing concentrations of isoflurane.
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Affiliation(s)
- I A Langmoen
- Institute for Surgical Research, Rikshospitalet, University of Oslo, Norway
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42
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Berg-Johnsen J, Langmoen IA. The effect of isoflurane on excitatory synaptic transmission in the rat hippocampus. Acta Anaesthesiol Scand 1992; 36:350-5. [PMID: 1317634 DOI: 10.1111/j.1399-6576.1992.tb03480.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The purpose of this investigation was to study the effect of isoflurane on excitatory synaptic transmission. Rat hippocampal slices maintained in vitro were used as a model. Isoflurane caused a dose-dependent reduction of the excitatory postsynaptic potential (EPSP); 1.5% isoflurane reduced the EPSP by 35 +/- 9% (mean +/- s.d.) and 3% by 57 +/- 11%. Neither spontaneous nor potassium-stimulated efflux of the glutamate analogue D-(3H)aspartate was changed, but the content of D-(3H)aspartate in slices loaded during isoflurane was reduced to 83 +/- 12% of control (P less than 0.05). The intracellularly recorded response to direct application of glutamate increased by 37 +/- 20% during isoflurane (3%) and 50 +/- 5% during halothane (2%). Isoflurane (3%) enhanced the response to the glutamate receptor agonist quisqualate by 44 +/- 19%, whereas the N-methyl-D-aspartate response was unchanged. Isoflurane enhanced the tetanic depression of the population spike. The present results suggest that isoflurane reduces excitatory synaptic transmission by a presynaptic mechanism.
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Affiliation(s)
- J Berg-Johnsen
- Institute for Experimental Medical Research, Ullevål Hospital, Oslo, Norway
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Stone JL, Ghaly RF, Levy WJ, Kartha R, Krinsky L, Roccaforte P. A comparative analysis of enflurane anesthesia on primate motor and somatosensory evoked potentials. ACTA ACUST UNITED AC 1992; 84:180-7. [PMID: 1372233 DOI: 10.1016/0168-5597(92)90023-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The effect of increasing enflurane concentration on magnetic-induced myogenic cranial (Cr) and peripheral (Pr) motor evoked potentials (MEPs), and electrically induced median (MN) and posterior tibial (PTN) somatosensory evoked potentials (SEPs) was studied in 10 monkeys. MEP, recorded from abductor pollicis brevis and abductor hallucis muscles, and SEP (short- and long-latency scalp recorded potentials) variables were examined at 0.25, 0.5, 0.75, 1.0 MAC enflurane concentrations. Cr-MEPs progressively attenuated (P less than 0.01) with 0.25 MAC and were abolished (greater than or equal to 0.75 MAC) by graded enflurane concentration. Stimulation threshold for Cr-MEP was progressively elevated (P less than 0.01), and eventually reliable responses were lost (greater than or equal to 0.75 MAC). Marked scalp zone reduction to obtain Cr-MEP responses was noted with increasing enflurane concentration. Pr-MEPs and most SEP peaks maintained good replicability but showed significant amplitude reduction (P less than 0.01). MEP and SEP latency values were not significantly delayed as long as the wave form remained identifiable. We conclude that enflurane has a differential influence on Cr-MEPs and SEPs. Administration of enflurane should be discouraged while monitoring myogenic Cr-MEPs since even a subanesthetic concentration is profoundly detrimental.
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Affiliation(s)
- J L Stone
- Department of Neurological Surgery, Cook County Hospital, Chicago, IL 60612
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Mantz J. Effets des anesthésiques intraveineux sur les neurones du système nerveux central : mécanismes d'action cellulaires et moléculaires. ACTA ACUST UNITED AC 1992; 11:540-57. [PMID: 1362044 DOI: 10.1016/s0750-7658(05)80761-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The mechanisms of action of intravenous anaesthetics are not yet completely elucidated. Until recently, most of the studies had focused on the interactions between anaesthetics and lipid bilayers. It has been proposed that loss of consciousness is produced by disorganization of the lipid phase of nerve membranes, which impairs the action potential propagation. However, new data obtained with sophisticated neuropharmacological tools such as the patch clamp technique have recently contributed to challenge this hypothesis. Indeed, several lines of evidence suggest that intravenous anaesthetics are thought to induce loss of consciousness by blocking the excitatory synaptic transmission. This can be achieved presynaptically, by inhibiting glutamate release from nerve endings via alterations in the gating properties of voltage-dependent calcium channels. Blockade of excitatory synaptic transmission can also occur at the postsynaptic level by antagonizing the glutamate receptors of the N-methyl D-aspartate subtype. Some anaesthetic agents including ketamine also block the nicotinic receptors, however the relevance of this finding with respect to clinical anaesthesia requires further investigation. Preliminary data also suggest that propofol and etomidate elicit uncoupling of gap junctions between astrocytes, which represent a major nonneuronal cell population in the central nervous system. This phenomenon might indirectly contribute to the hypnotic action of these compounds. Whether loss of consciousness involves preferential target structures within the brain remains to be delineated. A better understanding of the mechanisms of action of general anaesthetics might contribute to generate new agents with more pharmacological selectivity and less undesirable side-effects.
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Affiliation(s)
- J Mantz
- Département d'Anesthésie et de Réanimation Chirurgicale, Hôpital Bichat-Claude-Bernard, Paris
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45
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Kyrklund T. The use of experimental studies to reveal suspected neurotoxic chemicals as occupational hazards: acute and chronic exposures to organic solvents. Am J Ind Med 1992; 21:15-24. [PMID: 1553982 DOI: 10.1002/ajim.4700210105] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The nervous system differs from many other body organs by its central control of vital functions and its low regeneration capacity. Organic solvents have, as a group, been suspected to have neurotoxic effects. Because of their similar physical properties and the fact that in industrial uses, they are often present in various mixtures, organic solvents have also been regarded, unfortunately, to induce common neurotoxic effects. However, it is evident from experimental studies using specified exposure conditions that different organic solvents have very diverse neurotoxic effects and also that the toxic mechanism may differ between acute and chronic exposure. No specific method used to describe a neurotoxic effect or single toxic response can be used for the overall occupational risk assessment of all organic solvents. Each solvent has to be considered as having its own unique toxic effects.
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Affiliation(s)
- T Kyrklund
- Institute of Neurobiology, University of Gothenburg, Sweden
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46
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Affiliation(s)
- J J Kendig
- Department of Anesthesia, Stanford University School of Medicine, California 94305-5123
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47
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Mody I, Tanelian DL, MacIver MB. Halothane enhances tonic neuronal inhibition by elevating intracellular calcium. Brain Res 1991; 538:319-23. [PMID: 1901506 DOI: 10.1016/0006-8993(91)90447-4] [Citation(s) in RCA: 81] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Whether the major action of anesthetics is to depress the central nervous system (CNS) by reducing excitation or enhancing inhibition remains unknown. Using whole cell patch-clamp recording in hippocampal slices, halothane and pentobarbital were found to prolong the decay time constant (TAU(D)) of GABAA-mediated spontaneous inhibitory postsynaptic currents (sIPSCs). Intracellular administration of the Ca2+ chelator BAPTA or the Ca2+ release inhibitor dantrolene significantly (ANOVA, P less than 0.005) reduced halothane's effect; in contrast, the pentobarbital effect was unchanged. Halothane induced depression of population spike amplitude was blocked by the GABAA antagonist bicuculline. Together, these findings suggest that a major depressant effect of halothane involves enhancement of GABAA-mediated inhibition through release of intraneuronally stored Ca2+.
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Affiliation(s)
- I Mody
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, CA 94305
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48
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Berg-Johnsen J, Langmoen IA. Mechanisms concerned in the direct effect of isoflurane on rat hippocampal and human neocortical neurons. Brain Res 1990; 507:28-34. [PMID: 2302577 DOI: 10.1016/0006-8993(90)90517-f] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The effect of isoflurane on postsynaptic neurons was studied by intracellular recordings from rat hippocampus and human neocortex in vitro. Isoflurane caused a hyperpolarization of the cell membrane. The hyperpolarization was reversed (although incompletely in some neurons) by increasing the membrane potential. The reversal potential was -80 +/- 12 mV (mean +/- S.D.) or 12 +/- 6 mV negative to the resting membrane potential. Potassium channel blockers reduced the isoflurane-induced hyperpolarization, while chloride loading was without effect. The transient depolarization preceding the hyperpolarization in some of the neurons was not reversed by hyperpolarization. The action potential was prolonged by 19 +/- 3% due to a slower rate of rise. The rise time was almost doubled. Firing threshold was increased by 4 +/- 3 mV (relative to the reference electrode). Subthreshold inward rectification was reduced or abolished. Some cells showed subthreshold outward rectification during isoflurane administration. These results suggest that isoflurane depressed neuronal excitability by (1) hyperpolarizing the cell membrane, at least partly by an increase in potassium conductance, (2) slowing the rate of rise of the action potential, presumably due to interference with the fast sodium channel, (3) decreasing subthreshold inward rectification and (4) increasing firing threshold.
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Affiliation(s)
- J Berg-Johnsen
- University of Oslo, Department of Neurosurgery, Ullevaal Hospital, Norway
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49
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Kushima Y, Takeda K, Oh-Hashi Y, Nakagawa T, Kato T. The effects of anesthetics on the concentrations of cholecystokinin octapeptide sulfate-like immunoreactivity in rat brain regions. Neuropeptides 1989; 14:225-30. [PMID: 2622522 DOI: 10.1016/0143-4179(89)90050-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Cholecystokinin octapeptide sulfate-like immunoreactivity (CCK-8S-LI) was determined by radioimmunoassay in rat brain areas following injections of pentobarbital, halothane and chloral hydrate. Time-dependent changes in the concentrations of CCK-8S-LI were different between pentobarbital and chloral hydrate in all brain regions studied. After pentobarbital injection, CCK-8S-Li peaked at 30-60 min in the frontal cortex, nucleus accumbens, striatum and substantia nigra; after chloral hydrate injection, CCK-8S-LI peaked at 120 min in the hypothalamus, nucleus accumbens and substantia nigra. Both anesthetics induced almost the same sleeping times. Halothane inhalation caused increases in the concentrations of CCK-8S-LI in the amygdala and hippocampus. In addition, following intracardial perfusion of saline for 30 min after pentobarbital anesthesia, the concentrations of CCK-8S-LI increased in the nucleus accumbens, and decreased in the frontal cortex. These results suggest that since different anesthetics cause different changes in CCK levels, anesthetics affect studies of these neurons.
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Affiliation(s)
- Y Kushima
- Department of Life Chemistry, Tokyo Institute of Technology, Yokohama, Japan
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50
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Miu P, Puil E. Isoflurane-induced impairment of synaptic transmission in hippocampal neurons. Exp Brain Res 1989; 75:354-60. [PMID: 2542074 DOI: 10.1007/bf00247941] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The effects of anaesthetic applications of isoflurane were studied using intracellular recording techniques in 82 CA1 neurons of in vitro hippocampal slice preparations (guinea pigs). Various parameters of their excitabilities such as membrane electrical properties, action potentials evoked by intracellular current pulse injections and spike afterhyperpolarizations, as well as synaptic potentials evoked by electrical stimulation of stratum radiatum, were determined during bath perfusion of clinical concentrations of isoflurane which were measured with 19fluorine-nuclear magnetic resonance techniques. The vaporizer settings of 1-4% isoflurane corresponded to concentrations of 100 microM to 500 microM. Isoflurane applications did not produce consistent effects on the resting potentials or passive membrane properties. However, when spike-evoked synaptic activity was blocked by tetrodotoxin, isoflurane application induced a hyperpolarization (3-5 mV) without greatly affecting input conductance and the slopes of current-voltage relations. The threshold, amplitude and duration of single or multiple spikes evoked by current injections also were not greatly altered by isoflurane applications. However, marked reductions were observed in the amplitudes of the long-lasting hyperpolarizations following an evoked train of a constant number (4 or 5) of spikes. The amplitudes of excitatory postsynaptic potentials evoked by electrical stimulation of stratum radiatum were diminished markedly during isoflurane applications; these effects, like those on the afterhyperpolarizations, were closely dependent on the dose and duration of the application. Low doses (less than 1%) of isoflurane reduced the amplitudes of inhibitory postsynaptic potentials whereas higher doses (1-4%) increased their amplitudes and durations. The effects on afterhyperpolarizations and synaptic potentials could not be attributed to anaesthetic related changes in the resting potentials of the neurons.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- P Miu
- Department of Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, Vancouver, Canada
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