Effect of serotonin and acetylcholine on electrical activity of the isolated rabbit cortex

Neuronal isolation of the rabbit cerebral hemisphere shifts the EEG spectrum in the direction of slower processes. Application of acetylcholine to the cortex brings about EEG activation and appearance of the theta rhythm. Initially serotonin application is accompanied by the appearance of theta rhythm periods; during subsequent administration of the drug these periods are gradually substituted by slow delta waves. Combined application of serotonin and acetylcholine to the isolated cortex brings about bursts of high amplitude activity, abruptly substituted by "silent" phases. In contrast to the intact cortex, where serotonin brought about prolonged and rhythmic alternation on the EEG of phases of high amplitude activity and of silent periods, in the isolated cortex the bursts of activity of about 1 min duration appeared only after application of acetylcholine to the serotonin-saturated cortex. Repeated phases of activation were either absent or of short duration and were rapidly extinguished.