The neurochemical study of intra-operative awareness

为了阐明术中意识的神经化学基础，采用脑微透析方法研究了全身麻醉大鼠大脑皮层疼痛刺激下乙酰胆碱释放的变化。采用高效液相色谱法测定麻醉时和后爪皮下注射5%福尔马林4 h后大鼠肾外乙酰胆碱的含量。未麻醉动物乙酰胆碱释放量在注射福尔马林后30 ~ 45分钟达到峰值，为基础水平的2倍，随后逐渐下降至基础水平。氟烷、异氟烷、安氟烷或七氟烷麻醉1 MAC后，乙酰胆碱释放量分别显著降低至基础值的7%、16%、5%或21%。然而，在给予这些吸入麻醉剂的疼痛刺激时，乙酰胆碱释放没有明显变化。乙酰胆碱是中枢神经系统中主要的兴奋性神经递质之一。胆碱能神经元被认为在调节意识状态中起着重要作用，并且已经表明，在从清醒到睡眠的过渡中，中枢神经系统中的乙酰胆碱释放减少。因此，本研究的结果为术中意识的发生在吸入性麻醉药中比静脉麻醉药少提供了神经化学基础。

To clarify the neurochemical basis for intra-operative awareness, the changes of acetylcholine release by the painful stimulation in rat cerebral cortex during general anesthesia were studied using brain microdialysis. The contents in extracellar acetylcholine during anesthesia and after the 4 hours of 5% formalin injection subcutaneously at the hind paw were measured with high performance liquid chromatography.In non-anesthetized animals, the release of acetylcholine significantly increased to the twice of basal values with peak level at 30-45 minutes after formalin injection and then it gradually declined to the basal level. The acetylcholine release was significantly decreased by 1 MAC of halothane, isoflurane, enflurane, or sevoflurane anesthesia to 7, 16, 5, or 21% of basal values, respectively. However, no significant change of acetylcholine release was observed at the delivery of the pain stimulation under administration of these inhalation anesthetics.Acetylcholine is one of the major excitatory neurotransmitters in the central nervous system (CNS). Cholinergic neurons have been assumed to play an important role in regulating the state of consciousness, and it has been shown that acetylcholine release in the CNS decreases in the transition from wakefulness to sleep. Therefore, the results of this study provide the neurochemical basis for the fact that the occurrence of intra-operative awareness is less during the administration of inhalation anesthetics than intravenous one.