EFFECTS OF INHALATION ANESTHETICS ON THE RELEASE OF ACETYLCHOLINE IN THE RAT CEREBRAL-CORTEX IN-VIVO

By analysing the EEG, reticular multi-unit activity and behavioural ch anges, we have classified general anaesthetics into three groups: cent ral nervous system (CNS) depressant, CNS excitant and epileptogenic ag ents. Changes in CNS neural activity are associated with alteration in transmitter release. We have attempted to clarify the actions of wide ly used inhalation anaesthetics, such as isoflurane (CNS depressant), nitrous oxide (CNS excitant) and sevoflurane (epileptogenic) on acetyl choline (ACh) release in the cerebral cortex using brain microdialysis . ACh release was suppressed by isoflurane and sevoflurane in a dose-r elated manner but recovered on wash-out. There were no significant dif ferences between the effects of sevoflurane and isoflurane at the same MAC values. In contrast, ACh release was enhanced significantly by ni trous oxide. These findings indicate that the response of the cortical cholinergic cells to different anaesthetics reflects their neurophysi ological characteristics, that is whether they stimulate or suppress C NS neurones.