LATERAL PREOPTIC LESIONS VOID SLOW-WAVE SLEEP ENHANCED BY URIDINE BUTNOT BY MURAMYL DIPEPTIDE IN RATS

We investigated the site of action of two sleep-inducing substances, v iz.. muramyl dipeptide (MDP) and uridine. Localized electrolytic lesio ns were made bilaterally in the lateral preoptic hypothalamus (LPO) in rats and nocturnal 10-h i.c.v. infusions of MDP and uridine were perf ormed before and after the LPO lesions. MDP increased only slow-wave s leep (SWS) in both intact and LPO-lesioned rats. Uridine promoted both SWS and paradoxical sleep (PS) before the LPO lesions whereas it incr eased only PS after the lesions. These results suggest that the LPO is crucial for SWS-promoting action of uridine but not MDP.