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Sylvain-Bonfanti L, Page J, Arbelet-Bonnin D, Meimoun P, Grésillon É, Bouteau F, Laurenti P. [Anaesthesia, a process common to all living organisms]. Med Sci (Paris) 2023; 39:738-743. [PMID: 37943134 DOI: 10.1051/medsci/2023123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2023] Open
Abstract
Because of their interest in medicine, most studies of anaesthesia focus on the nervous system of metazoans, and the fact that any life form can be anaesthetised is often underlooked. If electrical signalling is an essential phenomenon for the success of animals, it appears to be widespread beyond metazoans. Indeed, anaesthesia targets Na+/Ca2+ voltage-gated channels that exist in a wide variety of species and originate from ancestral channels that predate eukaryotes in the course of evolution. The fact that the anaesthetic capacity that leads to loss of sensitivity is common to all phyla may lead to two hypotheses: to be investigated is the evolutionary maintenance of the ability to be anaesthetised due to an adaptive advantage or to a simple intrinsic defect in ion channels? The study of anaesthesia in organisms phylogenetically distant from animals opens up promising prospects for the discovery of new anaesthetic treatments. Moreover, it should also lead to a better understanding of a still poorly understood phenomenon that yet unifies all living organisms. We hope that this new understanding of the unity of life will help humans to assume their responsibilities towards all species, at a time when we are threatening biodiversity with mass extinction.
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Affiliation(s)
- Lucia Sylvain-Bonfanti
- Université Paris-Cité, laboratoire interdisciplinaire des énergies de demain (LIED UMR 8236), Paris, France - Université Paris-Cité, laboratoire dynamiques sociales et recomposition des espaces (LADYSS UMR 7533), Paris, France
| | - Julien Page
- Université Paris-Cité, laboratoire interdisciplinaire des énergies de demain (LIED UMR 8236), Paris, France
| | - Delphine Arbelet-Bonnin
- Université Paris-Cité, laboratoire interdisciplinaire des énergies de demain (LIED UMR 8236), Paris, France
| | - Patrice Meimoun
- Université Paris-Cité, laboratoire interdisciplinaire des énergies de demain (LIED UMR 8236), Paris, France - Sorbonne université, Paris, France
| | - Étienne Grésillon
- Université Paris-Cité, laboratoire dynamiques sociales et recomposition des espaces (LADYSS UMR 7533), Paris, France
| | - François Bouteau
- Université Paris-Cité, laboratoire interdisciplinaire des énergies de demain (LIED UMR 8236), Paris, France
| | - Patrick Laurenti
- Université Paris-Cité, laboratoire interdisciplinaire des énergies de demain (LIED UMR 8236), Paris, France
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Zhai X, Yuan Y, Xu L, Jun J, Li Y, Yan Y, Zhang L. Cerebrospinal fluid contacting nucleus and its 5-HT: A new insight into the regulation mechanism of general intravenous anesthesia. Brain Res 2022; 1798:148168. [DOI: 10.1016/j.brainres.2022.148168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2022] [Revised: 11/08/2022] [Accepted: 11/14/2022] [Indexed: 11/18/2022]
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3
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Jung J, Kim T. General anesthesia and sleep: like and unlike. Anesth Pain Med (Seoul) 2022; 17:343-351. [DOI: 10.17085/apm.22227] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Accepted: 10/17/2022] [Indexed: 11/05/2022] Open
Abstract
General anesthesia and sleep have long been discussed in the neurobiological context owingto their commonalities, such as unconsciousness, immobility, non-responsiveness to externalstimuli, and lack of memory upon returning to consciousness. Sleep is regulated bycomplex interactions between wake-promoting and sleep-promoting neural circuits. Anestheticsexert their effects partly by inhibiting wake-promoting neurons or activating sleep-promotingneurons. Unconscious but arousable sedation is more related to sleep-wake circuitries,whereas unconscious and unarousable anesthesia is independent of them. Generalanesthesia is notable for its ability to decrease sleep propensity. Conversely, increasedsleep propensity due to insufficient sleep potentiates anesthetic effects. Taken together, it isplausible that sleep and anesthesia are closely related phenomena but not the same ones.Further investigations on the relationship between sleep and anesthesia are warranted.
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Wang C, Liu S, Liu F, Bhutta A, Patterson TA, Slikker W. Application of Nonhuman Primate Models in the Studies of Pediatric Anesthesia Neurotoxicity. Anesth Analg 2022; 134:1203-1214. [PMID: 35147575 DOI: 10.1213/ane.0000000000005926] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Numerous animal models have been used to study developmental neurotoxicity associated with short-term or prolonged exposure of common general anesthetics at clinically relevant concentrations. Pediatric anesthesia models using the nonhuman primate (NHP) may more accurately reflect the human condition because of their phylogenetic similarity to humans with regard to reproduction, development, neuroanatomy, and cognition. Although they are not as widely used as other animal models, the contribution of NHP models in the study of anesthetic-induced developmental neurotoxicity has been essential. In this review, we discuss how neonatal NHP animals have been used for modeling pediatric anesthetic exposure; how NHPs have addressed key data gaps and application of the NHP model for the studies of general anesthetic-induced developmental neurotoxicity. The appropriate application and evaluation of the NHP model in the study of general anesthetic-induced developmental neurotoxicity have played a key role in enhancing the understanding and awareness of the potential neurotoxicity associated with pediatric general anesthetics.
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Affiliation(s)
- Cheng Wang
- From the Division of Neurotoxicology, National Center for Toxicological Research/FDA, Jefferson, Arkansas
| | - Shuliang Liu
- From the Division of Neurotoxicology, National Center for Toxicological Research/FDA, Jefferson, Arkansas
| | - Fang Liu
- From the Division of Neurotoxicology, National Center for Toxicological Research/FDA, Jefferson, Arkansas
| | - Adnan Bhutta
- Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Tucker A Patterson
- Office of the Director, National Center for Toxicological Research/FDA, Jefferson, Arkansas
| | - William Slikker
- Office of the Director, National Center for Toxicological Research/FDA, Jefferson, Arkansas
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George BM, Pandit JJ. General anaesthetics as 'awakening agents'? Re-appraising the evidence for suggested 'pressure reversal' of anaesthesia. Clin Exp Pharmacol Physiol 2021; 48:1454-1468. [PMID: 34309890 DOI: 10.1111/1440-1681.13554] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 07/06/2021] [Accepted: 07/19/2021] [Indexed: 11/30/2022]
Abstract
Increasing ambient pressure has been suggested to reverse general anaesthesia and provides support for the 'lipid theory'. Anaesthetic dissolution into cell membranes is said to cause their expansion to a critical volume. This triggers a sequence of events as basis of a unitary theory of anaesthestic mechanism. Pressure is argued to restore membrane volume to below critical level, reversing this process. We wished to review the original literature to assess internal consistency within and across papers, and to consider if alternative interpretations were possible. A literature search yielded 31 relevant 'pressure reversal' papers for narrative review, and 8 papers that allowed us to re-plot original data more consistently as 'dose-response' curves for the anaesthetics examined. Original studies were heterogenous for end-points, pressure ranges, species, and agents. Pressure effects were inconsistent, with narcosis at certain pressures and excitation at others, influenced by carrier gas (e.g., nitrogen vs helium). Pressure reversal (a right- or downward-shift on the re-plotted dose-response curves) was evident, but only in some species and at certain pressures and anaesthetic concentrations. However, even more striking was a novel 'awakening' effect of anaesthetics: i.e., anaesthetics reversed the narcotic effect of pressure, but this was limited to certain pressures at generally low anaesthetic concentrations. Contrary to the established view, 'pressure reversal' is not a universal phenomenon. The awakening effect of anaesthetics - described here for the first time - has equal evidence to support it, within the same literature, and is something that cannot be fully explained. Pressure cannot meaningfully be used to gain insight into anaesthetic mechanisms because of its heterogenous, non-specific and unpredictable effects on biological systems.
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Affiliation(s)
- Ben M George
- Nuffield Department of Anaesthetics, Oxford University Hospitals NHS Trust, Oxford, UK
| | - Jaideep J Pandit
- Nuffield Department of Anaesthetics, Oxford University Hospitals NHS Trust, Oxford, UK.,University of Oxford, Oxford, UK
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6
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Charalambous M, Volk HA, Van Ham L, Bhatti SFM. First-line management of canine status epilepticus at home and in hospital-opportunities and limitations of the various administration routes of benzodiazepines. BMC Vet Res 2021; 17:103. [PMID: 33663513 PMCID: PMC7934266 DOI: 10.1186/s12917-021-02805-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Accepted: 02/16/2021] [Indexed: 12/22/2022] Open
Affiliation(s)
- Marios Charalambous
- Small Animal Department, Faculty of Veterinary Medicine, Ghent University, 9820, Merelbeke, Belgium.
| | - Holger A Volk
- Department of Small Animal Medicine and Surgery, University of Veterinary Medicine Hannover, 30559, Hannover, Germany
| | - Luc Van Ham
- Small Animal Department, Faculty of Veterinary Medicine, Ghent University, 9820, Merelbeke, Belgium
| | - Sofie F M Bhatti
- Small Animal Department, Faculty of Veterinary Medicine, Ghent University, 9820, Merelbeke, Belgium
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Yang X, Luethy A, Zhang H, Luo Y, Xue Q, Yu B, Lu H. Mechanism and Development of Modern General Anesthetics. Curr Top Med Chem 2020; 19:2842-2854. [PMID: 31724504 DOI: 10.2174/1568026619666191114101425] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Revised: 08/09/2019] [Accepted: 08/12/2019] [Indexed: 01/01/2023]
Abstract
BACKGROUND Before October 1846, surgery and pain were synonymous but not thereafter. Conquering pain must be one of the very few strategies that has potentially affected every human being in the world of all milestones in medicine. METHODS This review article describes how various general anesthetics were discovered historically and how they work in the brain to induce sedative, hypnosis and immobility. Their advantages and disadvantages will also be discussed. RESULTS Anesthesia is a relatively young field but is rapidly evolving. Currently used general anesthetics are almost invariably effective, but nagging side effects, both short (e.g., cardiac depression) and long (e.g., neurotoxicity) term, have reawakened the call for new drugs. CONCLUSION Based on the deepening understanding of historical development and molecular targets and actions of modern anesthetics, novel general anesthetics are being investigated as potentially improved sedative-hypnotics or a key to understand the mechanism of anesthesia.
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Affiliation(s)
- Xiaoxuan Yang
- Department of Anesthesiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200025, China
| | - Anita Luethy
- Department of Anesthesia, Kantonsspital Aarau, Aarau, Switzerland
| | - Honghai Zhang
- Department of Anesthesiology, Affiliated Hangzhou First People's Hospital, Zhejiang University School of Medicine, Hangzhou, 310006, China
| | - Yan Luo
- Department of Anesthesiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200025, China
| | - Qingsheng Xue
- Department of Anesthesiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200025, China
| | - Buwei Yu
- Department of Anesthesiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200025, China
| | - Han Lu
- Department of Anesthesiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200025, China
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Pavlovič A, Libiaková M, Bokor B, Jakšová J, Petřík I, Novák O, Baluška F. Anaesthesia with diethyl ether impairs jasmonate signalling in the carnivorous plant Venus flytrap (Dionaea muscipula). ANNALS OF BOTANY 2020; 125:173-183. [PMID: 31677265 PMCID: PMC6948209 DOI: 10.1093/aob/mcz177] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 08/06/2019] [Accepted: 10/25/2019] [Indexed: 05/18/2023]
Abstract
BACKGROUND AND AIMS General anaesthetics are compounds that induce loss of responsiveness to environmental stimuli in animals and humans. The primary site of action of general anaesthetics is the nervous system, where anaesthetics inhibit neuronal transmission. Although plants do not have neurons, they generate electrical signals in response to biotic and abiotic stresses. Here, we investigated the effect of the general volatile anaesthetic diethyl ether on the ability to sense potential prey or herbivore attacks in the carnivorous plant Venus flytrap (Dionaea muscipula). METHODS We monitored trap movement, electrical signalling, phytohormone accumulation and gene expression in response to the mechanical stimulation of trigger hairs and wounding under diethyl ether treatment. KEY RESULTS Diethyl ether completely inhibited the generation of action potentials and trap closing reactions, which were easily and rapidly restored when the anaesthetic was removed. Diethyl ether also inhibited the later response: jasmonic acid (JA) accumulation and expression of JA-responsive genes (cysteine protease dionain and type I chitinase). However, external application of JA bypassed the inhibited action potentials and restored gene expression under diethyl ether anaesthesia, indicating that downstream reactions from JA are not inhibited. CONCLUSIONS The Venus flytrap cannot sense prey or a herbivore attack under diethyl ether treatment caused by inhibited action potentials, and the JA signalling pathway as a consequence.
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Affiliation(s)
- Andrej Pavlovič
- Department of Biophysics, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University, Šlechtitelů, Olomouc, Czech Republic
| | - Michaela Libiaková
- Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, Mlynská dolina, Bratislava, Slovakia
| | - Boris Bokor
- Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, Mlynská dolina, Bratislava, Slovakia
- Comenius University Science Park, Comenius University in Bratislava, Ilkovičova, Bratislava, Slovakia
| | - Jana Jakšová
- Department of Biophysics, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University, Šlechtitelů, Olomouc, Czech Republic
| | - Ivan Petřík
- Laboratory of Growth Regulators, Faculty of Science, Palacký University and Institute of Experimental Botany of the Czech Academy of Sciences, Šlechtitelů, Olomouc, Czech Republic
| | - Ondřej Novák
- Laboratory of Growth Regulators, Faculty of Science, Palacký University and Institute of Experimental Botany of the Czech Academy of Sciences, Šlechtitelů, Olomouc, Czech Republic
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Bodnar J. The Use of Propofol for Continuous Deep Sedation at the End of Life: A Definitive Guide. J Pain Palliat Care Pharmacother 2019; 33:63-81. [DOI: 10.1080/15360288.2019.1667941] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- John Bodnar
- John Bodnar, Penn Hospice at Chester County, West Chester, Pennsylvania, USA
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10
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Zebrafish behavioural profiling identifies GABA and serotonin receptor ligands related to sedation and paradoxical excitation. Nat Commun 2019; 10:4078. [PMID: 31501447 PMCID: PMC6733874 DOI: 10.1038/s41467-019-11936-w] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Accepted: 08/13/2019] [Indexed: 02/08/2023] Open
Abstract
Anesthetics are generally associated with sedation, but some anesthetics can also increase brain and motor activity—a phenomenon known as paradoxical excitation. Previous studies have identified GABAA receptors as the primary targets of most anesthetic drugs, but how these compounds produce paradoxical excitation is poorly understood. To identify and understand such compounds, we applied a behavior-based drug profiling approach. Here, we show that a subset of central nervous system depressants cause paradoxical excitation in zebrafish. Using this behavior as a readout, we screened thousands of compounds and identified dozens of hits that caused paradoxical excitation. Many hit compounds modulated human GABAA receptors, while others appeared to modulate different neuronal targets, including the human serotonin-6 receptor. Ligands at these receptors generally decreased neuronal activity, but paradoxically increased activity in the caudal hindbrain. Together, these studies identify ligands, targets, and neurons affecting sedation and paradoxical excitation in vivo in zebrafish. Some anesthetics despite being generally associated with sedation, can also increase brain activity—a phenomenon called paradoxical excitation. The authors identified dozens of compounds that generally decrease neuronal activity, but increase activity in the caudal hindbrain of zebrafish.
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Enger R, Dukefoss DB, Tang W, Pettersen KH, Bjørnstad DM, Helm PJ, Jensen V, Sprengel R, Vervaeke K, Ottersen OP, Nagelhus EA. Deletion of Aquaporin-4 Curtails Extracellular Glutamate Elevation in Cortical Spreading Depression in Awake Mice. Cereb Cortex 2017; 27:24-33. [PMID: 28365776 PMCID: PMC5939213 DOI: 10.1093/cercor/bhw359] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Revised: 10/25/2016] [Accepted: 10/29/2016] [Indexed: 12/20/2022] Open
Abstract
Cortical spreading depression (CSD) is a phenomenon that challenges the homeostatic mechanisms on which normal brain function so critically depends. Analyzing the sequence of events in CSD holds the potential of providing new insight in the physiological processes underlying normal brain function as well as the pathophysiology of neurological conditions characterized by ionic dyshomeostasis. Here, we have studied the sequential progression of CSD in awake wild-type mice and in mice lacking aquaporin-4 (AQP4) or inositol 1,4,5-triphosphate type 2 receptor (IP3R2). By the use of a novel combination of genetically encoded sensors that a novel combination - an unprecedented temporal and spatial resolution, we show that CSD leads to brisk Ca2+ signals in astrocytes and that the duration of these Ca2+ signals is shortened in the absence of AQP4 but not in the absence of IP3R2. The decrease of the astrocytic, AQP4-dependent Ca2+ signals, coincides in time and space with a decrease in the duration of extracellular glutamate overflow but not with the initial peak of the glutamate release suggesting that in CSD, extracellular glutamate accumulation is extended through AQP4-dependent glutamate release from astrocytes. The present data point to a salient glial contribution to CSD and identify AQP4 as a new target for therapy.
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Affiliation(s)
- Rune Enger
- Department of Neurology, Oslo University Hospital, N-0027 Oslo, Norway
- GliaLab and Letten Centre, Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
| | - Didrik B. Dukefoss
- GliaLab and Letten Centre, Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
| | - Wannan Tang
- GliaLab and Letten Centre, Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
| | - Klas H. Pettersen
- GliaLab and Letten Centre, Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
| | - Daniel M. Bjørnstad
- GliaLab and Letten Centre, Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
| | - P. Johannes Helm
- GliaLab and Letten Centre, Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
| | - Vidar Jensen
- GliaLab and Letten Centre, Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
| | - Rolf Sprengel
- Department of Molecular Neurobiology, Max Planck Institute for Medical Research, D-69120 Heidelberg, Germany
- Max Planck Research Group at the Institute for Anatomy and Cell Biology, Heidelberg University, D-69120 Heidelberg, Germany
| | - Koen Vervaeke
- Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
| | - Ole P. Ottersen
- Division of Anatomy, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
| | - Erlend A. Nagelhus
- Department of Neurology, Oslo University Hospital, N-0027 Oslo, Norway
- GliaLab and Letten Centre, Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
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12
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Walker MC. Pathophysiology of status epilepticus. Neurosci Lett 2016; 667:84-91. [PMID: 28011391 DOI: 10.1016/j.neulet.2016.12.044] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 12/16/2016] [Accepted: 12/17/2016] [Indexed: 12/22/2022]
Abstract
Status epilepticus (SE) is the maximal expression of epilepsy with a high morbidity and mortality. It occurs due to the failure of mechanisms that terminate seizures. Both human and animal data indicate that the longer a seizure lasts, the less likely it is to stop. Recent evidence suggests that there is a critical transition from an ictal to a post-ictal state, associated with a transition from a spatio-temporally desynchronized state to a highly synchronized state, respectively. As SE continues, it becomes progressively resistant to drugs, in particular benzodiazepines due partly to NMDA receptor-dependent internalization of GABA(A) receptors. Moreover, excessive calcium entry into neurons through excessive NMDA receptor activation results in activation of nitric oxide synthase, calpains, and NADPH oxidase. The latter enzyme plays a critical part in the generation of seizure-dependent reactive oxygen species. Calcium also accumulates in mitochondria resulting in mitochondrial failure (decreased ATP production), and opening of the mitochondrial permeability transition pore. Together these changes result in status epilepticus-dependent neuronal death via several pathways. Multiple downstream mechanisms including inflammation, break down of the blood-brain barrier, and changes in gene expression can contribute to later pathological processes including chronic epilepsy and cognitive decline.
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Affiliation(s)
- Matthew C Walker
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London WC1N 3BG, United Kingdom.
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Walters JL, Chelonis JJ, Fogle CM, Orser BA, Paule MG. Single and repeated exposures to the volatile anesthetic isoflurane do not impair operant performance in aged rats. Neurotoxicology 2016; 56:159-169. [PMID: 27498192 DOI: 10.1016/j.neuro.2016.07.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Revised: 07/27/2016] [Accepted: 07/29/2016] [Indexed: 01/12/2023]
Abstract
Postoperative Cognitive Dysfunction (POCD) is a complication that can occur in the elderly after anesthesia and surgery and is characterized by impairments in information processing, memory, and executive function. Currently, it is unclear whether POCD is due to the effects of surgery, anesthesia, or perhaps some interaction between these or other perioperative variables. Studies in rodents suggest that the development of POCD may be related directly to anesthesia-induced neuroactivity. Volatile anesthetics have been shown to increase cellular inflammation and apoptosis within the hippocampus of aged rodents, while producing corresponding impairments in hippocampal-dependent brain functions. However, it is unclear whether volatile anesthetics can affect additional aspects of cognition that do not primarily depend upon the hippocampus. The purpose of this study was to use established operant tests to examine the effects of isoflurane on aspects of behavioral inhibition, learning, and motivation in aged rats. Twenty-one adult Sprague-Dawley rats (11 male, 10 female) were trained to perform fixed consecutive number (FCN), incremental repeated acquisition (IRA), and progressive ratio (PR) tasks for a minimum of 15 months prior to receiving anesthesia. At 23 months of age, rats were exposed to 1.3% isoflurane or medical grade air for 2h. Initial results revealed that a 2h exposure to isoflurane had no effect on IRA, FCN, or PR performance. Thus, rats received 3 additional exposures to 1.3% isoflurane or medical grade air: 2, 4 and 6h exposures with 2 weeks elapsing before exposure two, 3 weeks elapsing between exposures two and three, and 2 weeks elapsing between exposures three and four. These additional exposures had no observable effects on performance of any operant task. These results suggest that single and repeated exposures to isoflurane do not impair the performance of aged rats in tasks designed to measure behavioral inhibition, learning, and motivation. This lack of significant effect suggests that the impairments associated with isoflurane exposure may not generalize to all aspects of cognition, but may be selective to tasks that primarily measure spatial memory processes.
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Affiliation(s)
- Jennifer L Walters
- National Center for Toxicological Research (NCTR)/FDA, Division of Neurotoxicology, 3900 NCTR Road, Jefferson, AR 72079, United States.
| | - John J Chelonis
- National Center for Toxicological Research (NCTR)/FDA, Division of Neurotoxicology, 3900 NCTR Road, Jefferson, AR 72079, United States
| | - Charles M Fogle
- National Center for Toxicological Research (NCTR)/FDA, Division of Neurotoxicology, 3900 NCTR Road, Jefferson, AR 72079, United States
| | - Beverley A Orser
- University of Toronto, Department of Physiology, Medical Sciences Building, Room 3318, 1 Kings College Circle, Toronto, Ontario M5S1A8, Canada
| | - Merle G Paule
- National Center for Toxicological Research (NCTR)/FDA, Division of Neurotoxicology, 3900 NCTR Road, Jefferson, AR 72079, United States
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14
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Hoestgaard-Jensen K, O'Connor RM, Dalby NO, Simonsen C, Finger BC, Golubeva A, Hammer H, Bergmann ML, Kristiansen U, Krogsgaard-Larsen P, Bräuner-Osborne H, Ebert B, Frølund B, Cryan JF, Jensen AA. The orthosteric GABAA receptor ligand Thio-4-PIOL displays distinctly different functional properties at synaptic and extrasynaptic receptors. Br J Pharmacol 2014; 170:919-32. [PMID: 23957253 DOI: 10.1111/bph.12340] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 08/06/2013] [Accepted: 08/11/2013] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND AND PURPOSE Explorations into the heterogeneous population of native GABA type A receptors (GABAA Rs) and the physiological functions governed by the multiple GABAA R subtypes have for decades been hampered by the lack of subtype-selective ligands. EXPERIMENTAL APPROACH The functional properties of the orthosteric GABAA receptor ligand 5-(4-piperidyl)-3-isothiazolol (Thio-4-PIOL) have been investigated in vitro, ex vivo and in vivo. KEY RESULTS Thio-4-PIOL displayed substantial partial agonist activity at the human extrasynaptic GABAA R subtypes expressed in Xenopus oocytes, eliciting maximal responses of up to ∼30% of that of GABA at α5 β3 γ2S , α4 β3 δ and α6 β3 δ and somewhat lower efficacies at the corresponding α5 β2 γ2S , α4 β2 δ and α6 β2 δ subtypes (maximal responses of 4-12%). In contrast, it was an extremely low efficacious agonist at the α1 β3 γ2S , α1 β2 γ2S , α2 β2 γ2S , α2 β3 γ2S , α3 β2 γ2S and α3 β3 γ2S GABAA Rs (maximal responses of 0-4%). In concordance with its agonism at extrasynaptic GABAA Rs and its de facto antagonism at the synaptic receptors, Thio-4-PIOL elicited robust tonic currents in electrophysiological recordings on slices from rat CA1 hippocampus and ventrobasal thalamus and antagonized phasic currents in hippocampal neurons. Finally, the observed effects of Thio-4-PIOL in rat tests of anxiety, locomotion, nociception and spatial memory were overall in good agreement with its in vitro and ex vivo properties. CONCLUSION AND IMPLICATIONS The diverse signalling characteristics of Thio-4-PIOL at GABAA Rs represent one of the few examples of a functionally subtype-selective orthosteric GABAA R ligand reported to date. We propose that Thio-4-PIOL could be a useful pharmacological tool in future studies exploring the physiological roles of native synaptic and extrasynaptic GABAA Rs.
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Affiliation(s)
- K Hoestgaard-Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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15
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Deeb TZ, Nakamura Y, Frost GD, Davies PA, Moss SJ. Disrupted Cl(-) homeostasis contributes to reductions in the inhibitory efficacy of diazepam during hyperexcited states. Eur J Neurosci 2013; 38:2453-67. [PMID: 23627375 PMCID: PMC3735799 DOI: 10.1111/ejn.12241] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Revised: 03/29/2013] [Accepted: 03/31/2013] [Indexed: 11/28/2022]
Abstract
The K(+) -Cl(-) cotransporter type 2 is the major Cl(-) extrusion mechanism in most adult neurons. This process in turn leads to Cl(-) influx upon activation of γ-aminobutyric acid type A (GABAA ) receptors and the canonical hyperpolarising inhibitory postsynaptic potential. Several neurological disorders are treated with drugs that target and enhance GABAA receptor signaling, including the commonly used benzodiazepine diazepam and the anesthetic propofol. Some of these disorders are also associated with deficits in GABAA signaling and become less sensitive to therapeutic drugs that target GABAA receptors. To date, it is unknown if alterations in the neuronal Cl(-) gradient affect the efficacies of diazepam and propofol. We therefore used the in vitro model of glutamate-induced hyperexcitability to test if alterations in the Cl(-) gradient affect the efficacy of GABAA modulators. We exclusively utilised the gramicidin perforated-patch-clamp configuration to preserve the endogenous Cl(-) gradient in rat neurons. Brief exposure to glutamate reduced the inhibitory efficacy of diazepam within 5 min, which was caused by the collapse of the Cl(-) gradient, and not due to reductions in GABAA receptor number. Unlike diazepam, propofol retained its efficacy by shunting the membrane conductance despite the glutamate-induced appearance of depolarising GABAA -mediated currents. Similarly, pharmacological inhibition of K(+) -Cl(-) cotransporter type 2 by furosemide disrupted Cl(-) homeostasis and reduced the efficacy of diazepam but not propofol. Collectively our results suggest that pathological hyperexcitable conditions could cause the rapid accumulation of intracellular Cl(-) and the appearance of depolarising GABAA -mediated currents that would decrease the efficacy of diazepam.
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Affiliation(s)
- Tarek Z Deeb
- Department of Neuroscience, Tufts University, Boston, MA, USA
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16
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Son Y. Molecular mechanisms of general anesthesia. Korean J Anesthesiol 2010; 59:3-8. [PMID: 20651990 PMCID: PMC2908224 DOI: 10.4097/kjae.2010.59.1.3] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2010] [Revised: 03/23/2010] [Accepted: 03/23/2010] [Indexed: 12/11/2022] Open
Abstract
General anesthetics produce a widespread neurodepression in the central nervous system by enhancing inhibitory neurotransmission and reducing excitatory neurotransmission. However, the action mechanisms of general anesthetics are not completely understood. Moreover, the general anesthetic state comprises multiple components (amnesia, unconsciousness, analgesia, and immobility), each of which is mediated by different receptors and neuronal pathways. Recently, neurotransmitter- and voltage-gated ion channels have emerged as the most likely molecular targets for general anesthetics. The γ-aminobutyric acid type A (GABAA) receptors are leading candidates as a primary target of general anesthetics. This review summarizes current knowledge on how anesthetics modify GABAA receptor function.
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Affiliation(s)
- Yong Son
- Department of Anesthesiology and Pain Medicine, Wonkwang University School of Medicine, Iksan, Korea
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17
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Jensen AA, Bergmann ML, Sander T, Balle T. Ginkgolide X is a potent antagonist of anionic Cys-loop receptors with a unique selectivity profile at glycine receptors. J Biol Chem 2010; 285:10141-10153. [PMID: 20106969 DOI: 10.1074/jbc.m109.079319] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The novel ginkgolide analog ginkgolide X was characterized functionally at human glycine and gamma-aminobutyric acid type A receptors (GlyRs and GABA(A)Rs, respectively) in the fluorescence-based FLIPR(TM) Membrane Potential assay. The compound inhibited the signaling of all GABA(A)R subtypes included in the study with high nanomolar/low micromolar IC(50) values, except the rho 1 receptor at which it was a significantly weaker antagonist. Ginkgolide X also displayed high nanomolar/low micromolar IC(50) values at the homomeric alpha1 and alpha2 GlyRs, whereas it was inactive at the heteromeric alpha 1 beta and alpha 2 beta subtypes at concentrations up to 300 microm. Thus, the functional properties of the compound were significantly different from those of the naturally occurring ginkgolides A, B, C, J, and M but similar to those of picrotoxin. In a mutagenesis study the 6' M2 residues in the GlyR ion channel were identified as the primary molecular determinant of the selectivity profile of ginkgolide X, and a 6' M2 ring consisting of five Thr residues was found to be of key importance for its activity at the GABA(A)R. Conformational analysis and docking of low-energy conformations of the native ginkgolide A and ginkgolide X into a alpha1 GlyR homology model revealed two distinct putative binding sites formed by the 6' M2 residues together with the 2' residues and the 10' and 13' residues, respectively. Thus, we propose that the distinct functionalities of ginkgolide X compared with the other ginkgolides could arise from different flexibility and thus different binding modes to the ion channel of the anionic Cys-loop receptor.
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Affiliation(s)
- Anders A Jensen
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
| | - Marianne L Bergmann
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Tommy Sander
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Thomas Balle
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
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18
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Jin YH, Zhang Z, Mendelowitz D, Andresen MC. Presynaptic actions of propofol enhance inhibitory synaptic transmission in isolated solitary tract nucleus neurons. Brain Res 2009; 1286:75-83. [PMID: 19559683 DOI: 10.1016/j.brainres.2009.06.058] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2009] [Revised: 06/17/2009] [Accepted: 06/18/2009] [Indexed: 10/20/2022]
Abstract
General anesthetics variably enhance inhibitory synaptic transmission that relies on (-aminobutyric acid (GABA) and GABAA receptor function with distinct differences across brain regions. Activation of "extra-synaptic" GABAA receptors produces a tonic current considered the most sensitive target for general anesthetics, particularly in forebrain neurons. To evaluate the contribution of poor drug access to neurons in slices, we tested the intravenous anesthetic propofol in mechanically isolated neurons from the solitary tract nucleus (NTS). Setting chloride concentrations to ECl=-29 mV made GABA currents inward at holding potentials of -60 mV. Propofol triggered pronounced but slowly-developing tonic currents that reversed with 5 min washing. Effective concentrations in isolated cells were lower than in slices and propofol enhanced phasic IPSCs more potently than tonic currents (1 microM increased phasic decay-time constant vs. >3 microM tonic currents). Propofol increased IPSC frequency (>3 microM), a presynaptic action. Bicuculline blocked all propofol actions. Gabazine blocked only phasic IPSCs. IPSCs persisted in TTX and/or cadmium but these agents prevented propofol-induced increases in IPSC frequency. Furosemide (>1 mM) reversibly blocked propofol-evoked IPSC frequency changes without altering waveforms. We conclude that presynaptic actions of propofol depend on a depolarizing chloride gradient across presynaptic inhibitory terminals. Our results in isolated neurons indicate that propofol pharmacokinetics intrinsically trigger the tonic currents slowly and the time course is not related to slow permeation or delivery. Unlike forebrain, phasic NTS GABAA receptors are more sensitive to propofol than tonic receptors but that presynaptic GABAA receptor mechanisms regulate GABA release.
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Affiliation(s)
- Young-Ho Jin
- Department of Physiology, Kyung Hee University, Seoul 130-701, Republic of Korea
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19
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Qiu M, Ramani R, Swetye M, Rajeevan N, Constable RT. Anesthetic effects on regional CBF, BOLD, and the coupling between task-induced changes in CBF and BOLD: an fMRI study in normal human subjects. Magn Reson Med 2009; 60:987-96. [PMID: 18816821 DOI: 10.1002/mrm.21759] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Functional MR imaging was performed in sixteen healthy human subjects measuring both regional cerebral blood flow (CBF) and blood oxygen level dependent (BOLD) signal when visual and auditory stimuli were presented to subjects in the presence or absence of anesthesia. During anesthesia, 0.25 mean alveolar concentration (MAC) sevoflurane was administrated. We found that low-dose sevoflurane decreased the task-induced changes in both BOLD and CBF. Within the visual and auditory regions of interest inspected, both baseline CBF and the task-induced changes in CBF decreased significantly during anesthesia. Low-dose sevoflurane significantly altered the task-induced CBF-BOLD coupling; for a unit change of CBF, a larger change in BOLD was observed in the anesthesia condition than in the anesthesia-free condition. Low-dose sevoflurane was also found to have significant impact on the spatial nonuniformity of the task-induced coupling. The alteration of task-induced CBF-BOLD coupling by low-dose sevoflurane introduces ambiguity to the direct interpretation of functional MRI (fMRI) data based on only one of the indirect measures-CBF or BOLD. Our observations also indicate that the manipulation of the brain with an anesthetic agent complicates the model-based quantitative interpretation of fMRI data, in which the relative task-induced changes in oxidative metabolism are calculated by means of a calibrated model given the relative changes in the indirect vascular measures, usually CBF and BOLD.
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Affiliation(s)
- Maolin Qiu
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut 06520-2048, USA.
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20
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GABA in the female brain — Oestrous cycle-related changes in GABAergic function in the periaqueductal grey matter. Pharmacol Biochem Behav 2008; 90:43-50. [DOI: 10.1016/j.pbb.2007.12.014] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2007] [Revised: 11/23/2007] [Accepted: 12/03/2007] [Indexed: 11/22/2022]
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21
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McDougall SJ, Bailey TW, Mendelowitz D, Andresen MC. Propofol enhances both tonic and phasic inhibitory currents in second-order neurons of the solitary tract nucleus (NTS). Neuropharmacology 2007; 54:552-63. [PMID: 18082229 DOI: 10.1016/j.neuropharm.2007.11.001] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2007] [Revised: 10/26/2007] [Accepted: 11/04/2007] [Indexed: 02/07/2023]
Abstract
The anesthetic propofol is thought to induce rapid hypnotic sedation by facilitating a GABAergic tonic current in forebrain neurons. The depression of cardiovascular and respiratory regulation often observed during propofol suggests potential additional actions within the brainstem. Here we determined the impacts of propofol on both GABAergic and glutamatergic synaptic mechanisms in a class of solitary tract nucleus (NTS) neurons common to brainstem reflex pathways. In horizontal brainstem slices, we recorded from NTS neurons directly activated by solitary tract (ST) axons. We identified these second-order NTS neurons by time-invariant ("jitter"<200 micros), "all-or-none" glutamatergic excitatory postsynaptic currents (EPSCs) in response to shocks to the ST. In order to assess propofol actions, we measured ST-evoked, spontaneous and miniature EPSCs and inhibitory postsynaptic currents (IPSCs) during propofol exposure. Propofol prolonged miniature IPSC decay time constants by 50% above control at 1.8 microM. Low concentrations of gabazine (SR-95531) blocked phasic GABA currents. At higher concentrations, propofol (30 microM) induced a gabazine-insensitive tonic current that was blocked by picrotoxin or bicuculline. In contrast, total propofol concentrations up to 30 microM had no effect on EPSCs. Thus, propofol enhanced phasic GABA events in NTS at lower concentrations than tonic current induction, opposite to the relative sensitivity observed in forebrain regions. These data suggest that therapeutic levels of propofol facilitate phasic (synaptic) inhibitory transmission in second-order NTS neurons which likely inhibits autonomic reflex pathways during anesthesia.
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Affiliation(s)
- Stuart J McDougall
- Department of Physiology and Pharmacology L334, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland OR 97239-3098, USA.
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22
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van Broekhoven F, Bäckström T, van Luijtelaar G, Buitelaar JK, Smits P, Verkes RJ. Effects of allopregnanolone on sedation in men, and in women on oral contraceptives. Psychoneuroendocrinology 2007; 32:555-64. [PMID: 17470385 DOI: 10.1016/j.psyneuen.2007.03.009] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/22/2006] [Revised: 03/18/2007] [Accepted: 03/19/2007] [Indexed: 10/23/2022]
Abstract
Allopregnanolone is a known GABA(A) receptor agonist not previously given to men, or to women using oral contraceptives (OC). The effects of metabolites of sex hormones on the GABA(A) receptor are different between men and women. OC are known to change GABA(A) receptor subunit composition. These factors might play a role in the differential effect of allopregnanolone in men and women, and in women with or without OC. To study the sedative effect of and sensitivity to allopregnanolone in men and in women with OC, nine healthy men (mean age 24.6 years) and nine healthy women on OC (mean age 21.8 years) were given three, increasing, intravenous dosages (0.015, 0.03, and 0.045 mg/kg) of allopregnanolone. Saccadic eye velocity (SEV), subjective ratings, and electroencephalography (EEG) were used to evaluate the response to allopregnanolone. Repeated blood samples for analyses of serum allopregnanolone levels were drawn throughout the study day. Allopregnanolone decreased SEV more in women than in men, and increased subjective ratings of 'sedation'. The results in women on OC are similar to earlier results in women without OC. Subjective ratings of 'contentedness' decreased in men but increased in women. Serum levels of allopregnanolone were more highly increased in men compared to women. Other pharmacokinetic parameters were not different between sexes. On the EEG, beta power increased in men. In conclusion, men and women on OC reacted differently to allopregnanolone.
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Affiliation(s)
- F van Broekhoven
- Department of Psychiatry, Unit for Clinical Psychopharmacology and Neuropsychiatry, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
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23
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Xiao C, Zhou C, Li K, Ye JH. Presynaptic GABAA receptors facilitate GABAergic transmission to dopaminergic neurons in the ventral tegmental area of young rats. J Physiol 2007; 580:731-43. [PMID: 17303643 PMCID: PMC2075446 DOI: 10.1113/jphysiol.2006.124099] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2006] [Accepted: 01/30/2007] [Indexed: 12/18/2022] Open
Abstract
Gamma-aminobutyric acid A receptor (GABA(A)R)-mediated postsynaptic currents (IPSCs) were recorded from dopaminergic neurons of the ventral tegmental area of young rats in acute brain slices and from mechanically dissociated neurons. Low concentrations (0.1-0.3 microm) of muscimol, a selective GABA(A)R agonist, increased the amplitude, and reduced the paired pulse ratio of evoked IPSCs. Moreover, muscimol increased the frequency but not the amplitude of spontaneous IPSCs (sIPSCs). These data point to a presynaptic locus of muscimol action. It is interesting that 1 microm muscimol caused an inhibition of sIPSCs, which was reversed to potentiation by the GABA(B) receptor antagonist CGP52432. Isoguvacine, a selective GABA(A)R agonist that belongs to a different class, mimicked the effects of muscimol on sIPSCs: it increased them at low (
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Affiliation(s)
- Cheng Xiao
- Department of Anesthesiology, Pharmacology and Physiology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, 185 South Orange Avenue, Newark, NJ 07103, USA
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24
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O'Meara GF, Newman RJ, Fradley RL, Dawson GR, Reynolds DS. The GABA-A beta3 subunit mediates anaesthesia induced by etomidate. Neuroreport 2004; 15:1653-6. [PMID: 15232301 DOI: 10.1097/01.wnr.0000134842.56131.fe] [Citation(s) in RCA: 16] [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 i.v. agent etomidate exerts its anaesthetic actions through potentiation of gamma-aminobutyric acid-A receptors containing beta2 and beta3 subunits. It was recently shown that the beta2 subunit contributes to the sedative properties of etomidate, whereas the beta3 subunit is responsible for its anaesthetic properties. However, these studies evaluated anaesthetic effects in point mutation mice in which the effect of etomidate was decreased, but not abolished, at the beta2 subunit. Here we have used beta2 knockout mice to completely remove any contribution of the beta2 subunit to the effects of etomidate. Etomidate was equally anaesthetic in wildtype and knockout mice, thus further confirming that efficacy at the beta3 subunit only is sufficient to induce general anaesthesia.
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Affiliation(s)
- Gillian F O'Meara
- Merck Sharp & Dohme Research Laboratories, The Neuroscience Research Centre, Terlings Park, Harlow, Essex CM20 2QR, UK
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