INTRAPERITONEAL INJECTION OF CHOLECYSTOKININ ELICITS SLEEP IN RABBITS

Cholecystokinin (CCK) reduces food intake and promotes non-rapid-eye-movement sleep (NREMS) in rats. The purpose of present experiments was to determine if CCK is somnogenic in rabbits; another species in which CCK suppresses feeding. White New Zealand rabbits were treated intracerebroventricularly (ICV; 0.05, 0.5 and 2-mu-g) or intraperitoneally (IP; 2.5, 10 and 40-mu-g/kg) with CCK or saline, and sleep-wake activity and brain temperature (T(br)) were recorded for 6 h. Injections of 10 and 40-mu-g/kg CCK IP elicited a decrease in wakefulness and an increase in NREMS during the first hour postinjection. The hypnogenic effects were accompanied by a decrease in T(br). After the IP injection of a lower dose (2.5-mu-g/kg) a slight, nonsignificant increase in NREMS during the first hour postinjection was followed by a decrease in NREMS. ICV injections of CCK had relatively small inhibitory effects on sleep. We conclude that circulating, hormone CCK might be a hypnogenic signal with a peripheral site of action.