Effects of inhalation anaesthetics on the release of acetylcholine in the rat cerebral cortex in vivo.

By analysing the EEG, reticular multi-unit activity and behavioural changes, we have classified general anaesthetics into three groups: central nervous system (CNS) depressant, CNS excitant and epileptogenic agents. Changes in CNS neural activity are associated with alteration in transmitter release. We have attempted to clarify the actions of widely used inhalation anaesthetics, such as isoflurane (CNS depressant), nitrous oxide (CNS excitant) and sevoflurane (epileptogenic) on acetylcholine (ACh) release in the cerebral cortex using brain microdialysis. ACh release was suppressed by isoflurane and sevoflurane in a dose-related manner but recovered on wash-out. There were no significant differences between the effects of sevoflurane and isoflurane at the same MAC values. In contrast, ACh release was enhanced significantly by nitrous oxide. These findings indicate that the response of the cortical cholinergic cells to different anaesthetics reflects their neurophysiological characteristics, that is whether they stimulate or suppress CNS neurones.