EFFECTS OF ISOFLURANE ON IN-VIVO RELEASE OF ACETYLCHOLINE IN THE RAT CEREBRAL-CORTEX AND STRIATUM

Background: Acetylcholine (ACh) is one of the major excitatory neurotr ansmitters in the central nervous system, and changes in neural activi ty induced by anesthesia alter the release of ACh. However, the effect s of isoflurane, one of the most widely used volatile anesthetics, on ACh release are not known. The present study attempts to clarify the d ose-effect relationship of isoflurane on the in vivo release of ACh in rat brains. Methods: Changes in the extracellular concentration of AC h and choline in the cerebral cortex and striatum induced by 0.5, 1.0, and 1.5 minimum alveolar concentration (MAC) of isoflurane were deter mined using a brain microdialysis technique. Results: Results: In the cortex, the ACh release decreased to 30.8 +/- 10.1 (mean +/- SEM), 10. 2 +/- 4.1, and 8.1 +/- 2.9% of basal value by increasing doses of isof lurane, and in the striatum, to 73.3 +/- 4.4, 49.2 +/- 4.2, and 40.7 /- 4.5%. The ACh release rapidly recovered control levels with the dis continuance of isoflurane. Choline concentration was not changed signi ficantly by isoflurane except for a decrease to 74.8 +/- 4.6% in the s triatum by 0.5 MAC. In both the cortex and striatum, the choline conce ntration decreased with the discontinuance of isoflurane to 70.3 +/- 1 3.3, and 68.2 +/- 5.4%, respectively. Conclusion: The fact that all cl assic anesthetics reported previously, as well as isoflurane, reduce A Ch release supports the hypothesis;hat the suppression of cholinergic cells is, at least in part, one of the mechanisms of anesthesia.