The neurochemical study of intra-operative awareness

为阐明术中意识的神经化学基础，采用脑微透析技术研究了全麻期间痛刺激对大鼠大脑皮层乙酰胆碱释放的影响。用高效液相色谱法测定麻醉期间和后爪皮下注射5%福尔马林后4 h内囊外乙酰胆碱的含量，发现非麻醉动物在注射福尔马林后30-45 min，囊外乙酰胆碱的释放量显著增加，达基础值的2倍，然后逐渐下降至基础值。氟烷、异氟烷、安氟烷或七氟烷麻醉1 MAC时，乙酰胆碱释放量分别显著降低至基础值的7%、16%、5%或21%。乙酰胆碱是中枢神经系统（CNS）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重要作用，并且已经表明CNS中的乙酰胆碱释放在从觉醒到睡眠的过渡中减少。因此，本研究的结果提供了一个事实，即术中意识的发生率在吸入麻醉药比静脉给药时少的神经化学基础。

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.