Differential acute influence of medial and lateral preoptic areas on sleep-wakefulness in freely moving rats.

The role of preoptic area (POA) in sleep-wakefulness and related EEG changes is well established. Anatomically the area is divided into medial (mPOA) and lateral (IPOA) portions having different physiological functions. Knowledge regarding the differential role, if any, of those two areas in sleep and wakefulness was lacking in the literature. Therefore, an attempt was made in this study, to investigate the same systematically. Experiments were conducted during day and night in freely moving rats. Electrophysiological parameters defining sleep and wakefulness were recorded before and after reversible inactivation of those two areas separately by microinjection of a local anaesthetic, marcain. The responses were opposite in nature depending upon the time, day or night, when the anaesthetic was applied. During the day, anaesthetization induced wakefulness while during the night, sleep was precipitated. However, anaesthetization of both the areas though induced similar qualitative response, the degree of the responses differed significantly. The results suggest that the mPOA is more effective in maintaining tonic sleep while the IPOA is more potent in the maintenance of tonic wakefulness in the normal rats. The finding supports and fits well with the existing knowledge.