Anesthetics, GABA and the Injured Brain

描述(申请人提供)：围手术期中风仍然是手术中的主要风险。挥发性麻醉剂对实验性脑缺血有保护作用，但其机制尚不清楚。我们假设挥发性麻醉剂增强GABA能神经传递和增加CI-内流。这会使神经元超极化，延迟缺血去极化和钙离子内流的时间。这一假说来自于观察到挥发性麻醉剂增强GABAA受体，而GABAA拮抗剂荷包牡丹碱在体外逆转异氟醚的保护作用。我们还假设，挥发性麻醉剂的GABA能特性比谷氨酸受体拮抗特性对保护作用更重要。我们提出这些特定的目标：1)确定大鼠前脑缺血期间异氟醚保护的剂量效应/比较GABAA受体激动剂麝香酚的疗效/比较缺血去极化开始的时间和缺血前的脑代谢率；2)确定异氟醚对严重前脑缺血的神经保护是否是永久性的；3)比较选择性NMDA/AMPA受体拮抗剂和具有GABA能增强作用的异氟醚的相对神经保护作用；4)确定GABAA增强在异氟醚抗严重前脑缺血保护中的作用。对于特定的目的#4，我们将研究：a)异氟醚对前脑缺血或纹状体NMDA微量注射的保护是否被GABAA拮抗剂(氟乙基、荷包牡丹碱、氟马西尼)逆转，b)如果异氟醚延迟缺血诱导的钙内流，如果这一延迟被GABAA拮抗剂逆转，c)如果通过延长缺血持续时间来纠正这种延迟，等同地逆转神经保护，d)GABAAβ亚基靶向缺失(基因敲除)或纹状体反义寡核苷酸微注射对体内异氟烷保护的影响，e)异氟醚对丙二醛兴奋毒性或缺氧/葡萄糖缺乏的保护程度及其对CI摄取的影响F)GABAA、GABAB和士的宁敏感的甘氨酸受体拮抗剂逆转的程度，以及g)异氟醚和GABAA拮抗剂对NMDA刺激的突触神经小体CI-和Ca++摄取的关系。我们认为，已知对麻醉至关重要的挥发性麻醉剂的GABA能药理特性与赋予大脑保护的特性是相同的。

DESCRIPTION (provided by applicant): Perioperative stroke remains a major risk during surgery. Volatile anesthetics protect against experimental brain ischemia but the mechanism is not defined. We hypothesize that volatile anesthetics potentiate GABAergic neurotransmission and enhance CI- influx. This hyperpolarizes neurons delaying time to ischemic depolarization and Ca2++ influx. This hypothesis is derived from observations that volatile anesthetics potentiate GABAA receptors and bicuculline, a GABAA antagonist, reverses isoflurane protection in vitro. We also hypothesize that volatile anesthetic GABAergic properties are more important to protection than glutamate receptor antagonistic properties. We propose these Specific Aims: 1) Define a dose-response for isoflurane protection during rat forebrain ischemia/Compare with efficacy of muscimol, a GABAA receptor agonist/Compare with time to onset of ischemic depolarization and pre-ischemic cerebral metabolic rate; 2) Determine if isoflurane neuroprotection against severe forebrain ischemia is permanent; 3) Compare the relative neuroprotective effect of selective NMDA/AMPA receptor antagonism to isoflurane, which also possesses GABAergic potentiation; 4) Determine the role of GABAA potentiation in isoflurane protection against severe forebrain ischemia. For Specific Aim #4, we will examine: a) if isoflurane protection against forebrain ischemia or striatal NMDA microinjections is reversed by GABAA antagonists (flurothyl, bicuculline, flumazenil), b) if isoflurane delays time to ischemia induced Ca2++ influx and if this is reversed by GABAA antagonists, c) if correction for this delay, by extending ischemia duration, equivalently reverses neuroprotection, d) effects of GABAA beta subunit-targeted deletion (knockout) or striatal antisense oligonucleotide microinjection on in vivo isoflurane protection, e) the extent to which isoflurane provides protection in organotypic hippocampal slices against NMDA excitotoxicity or oxygen/glucose deprivation and respective effects on CI- uptake, f) the extent to which this is reversed by antagonists of the GABAA, GABAB, and strychnine sensitive glycine receptors, and g) relationships between isoflurane and GABAA antagonists on CI- and Ca ++uptake in NMDA stimulated synaptoneurosomes. We believe that GABAAergic pharmacologic properties of volatile anesthetics known to be critical for anesthesia are the same properties that confer cerebral protection.