Anesthetics, GABA and the Injured Brain

描述（由申请人提供）：围手术期卒中仍然是手术期间的主要风险。挥发性麻醉剂对实验性脑缺血有保护作用，但其机制尚不明确。我们推测挥发性麻醉药增强GABA能神经传递并增强CI-内流。这使神经元超极化，延迟缺血去极化和Ca 2 ++内流的时间。这一假设来源于挥发性麻醉剂增强GABAA受体和荷包牡丹碱（一种GABAA拮抗剂）在体外逆转异氟烷保护作用的观察结果。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。我们提出了以下具体目的：1）确定大鼠前脑缺血期间异氟醚保护作用的剂量反应/与蝇蕈醇（GABAA受体激动剂）的疗效比较/与缺血去极化发作时间和缺血前脑代谢率比较; 2）确定异氟醚对严重前脑缺血的神经保护作用是否持久; 3）比较选择性NMDA/AMPA受体拮抗剂与异氟醚的相对神经保护作用，异氟醚也具有GABA能增强作用; 4）确定GABAA增强在异氟醚对严重前脑缺血的保护中的作用。对于具体目标#4，我们将检查：a）如果异氟烷对前脑缺血或纹状体NMDA微量注射的保护作用被GABAA拮抗剂逆转，（氟甲氧乙基、荷包牡丹碱、氟马西尼），B）如果异氟烷延迟缺血诱导的Ca 2 ++内流的时间，并且如果这被GABAA拮抗剂逆转，c）如果通过延长缺血持续时间来校正该延迟，则等效地逆转神经保护，d）GABAA β亚基靶向缺失的影响（敲除）或纹状体反义寡核苷酸显微注射对体内异氟烷保护的影响，e）异氟烷在器官型海马切片中提供针对NMDA兴奋性毒性或氧/葡萄糖剥夺的保护的程度以及对Cl-摄取的相应影响，f）这被GABAA，GABAB，和士的宁敏感的甘氨酸受体，和g）异氟烷和GABAA拮抗剂对NMDA刺激的突触神经体中Cl-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药的GABA能药理学性质与赋予脑保护的性质相同。

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.