The effects of cholecystokinin octapeptide (CCK-8), cholecystokinin tetrapeptide amide (CCK-4), β-endorphin, proglumide, and naloxone on passive avoidance behavior were studied in rats. Intracerebroventricular (i.c. v.) injection of β-endorphin (1–10 μg) had no significant influence on the latency of the avoidance response in intact rats. Also, β-endorphin (0.05–5 μg, 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 μg, i.c.v.) on ECS-induced amnesia was partly antagonized by β-endorphin (0.05–10 μg, 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 μg, i.c.v.) and prevented it when induced by CCK-4 (5 and 10 μg, i.c.v.). The results indicate the facilitating action of naloxone and the inhibitory effect of β-endorphin on memory, suggesting that the endogenous opiate systems are involved in some way in the memory processes.
Effects of exogenous and endogenous opiate compounds on ion transport in rabbit ileum in vitro
