Interactions of cholecystokinin, beta-endorphin, and their antagonists on passive avoidance behavior in rats

The effects of cholecystokinin octapeptide (CCK-8), cholecystokinin tetrapeptide amide (CCK-4), beta-endorphin, proglumide, and naloxone on passive avoidance behavior were studied in rats. Intracerebroventricular (i.c.v.) injection of beta-endorphin (1-10 micrograms) had no significant influence on the latency of the avoidance response in intact rats. Also, beta-endorphin (0.05-5 micrograms, i.c.v.) did not affect the response in rats treated with electroconvulsive shock (ECS). The preventive effect of CCK-8 (0.1-1.0 micrograms, i.c.v.) on ECS-induced amnesia was partly antagonized by beta-endorphin (0.05-10 micrograms, i.c.v.). Intraperitoneal (i.p.) injection of naloxone (1-10 mg/kg) could not prevent ECS-induced amnesia, but continuous subcutaneous infusion of this drug (2 mg/day, 7 days) completely abolished the amnesia. Naloxone (1 and 10 mg/kg, i.p.) also partly antagonized amnesia induced by proglumide (1 and 10 micrograms, i.c.v.) and prevented it when induced by CCK-4 (5 and 10 micrograms, i.c.v.). The results indicate the facilitating action of naloxone and the inhibitory effect of beta-endorphin on memory, suggesting that the endogenous opiate systems are involved in some way in the memory processes.