MICRODIALYSIS MEASUREMENT OF CORTICAL AND HIPPOCAMPAL ACETYLCHOLINE-RELEASE DURING SLEEP-WAKE CYCLE IN FREELY MOVING CATS

The variations of Acetylcholine (ACh) release in the cerebral cortex a nd dorsal hippocampus were monitored by microdialysis during the elect roencephalographically recorded sleep-waking cycle in freely moving ca ts. The results show a state-dependent variation in ACh output in both the cortex and the hippocampus. ACh release increased by approximatel y 100% during quiet waking (QW) and by 175% during active waking (AW) as referred to slow wave sleep (SWS) baseline. In contrast, a clear di fference between the two areas was observed during REM sleep. During t his stage ACh release in the cortex reached approximately the same val ues observed during QW, while in the hippocampus ACh release rose to a bout 4-fold the level obtained during SWS or twice that of QW. The res ults support the idea that the increase in ACh release in the cortex r eflects the desynchronized EEG of wakefulness and REM sleep, while the marked increase of ACh during REM in the hippocampus may be related t o the sustained theta activity in this area.