RECIPROCAL INTERACTION OF 5-HYDROXYTRYPTAMINE AND CHOLECYSTOKININ IN THE CONTROL OF FEEDING PATTERNS IN RATS

1 The effect of the CCK(A) receptor antagonist, devazepide (100 mg kg-1) on meal parameters during the initial phase of the dark period was studied in free-feeding rats by use of a procedure for continuously monitoring feeding patterns. 2 In a second experiment, the effect of devazepide on the reduction in meal parameters induced by the 5-hydroxytryptamine (5-HT) releaser and uptake inhibitor, (+)-fenfluramine (1.5 mg kg-1) in 4 h food-deprived rats was examined. 3 The hypophagic effect of an intraperitoneal injection of cholecystokinin (CCK-8, 4 mug kg-1) was studied in rats treated with the 5-HT receptor antagonist, metergoline (1 and 2 mg kg-1). 4 Devazepide increased the size of the first meal in free-feeding, but not in 4 h food-deprived rats and partially antagonized the effect of (+)-fenfluramine on the size and duration of the first meal. The reduction in eating rate induced by (+)-fenfluramine was not modified by devazepide. No changes in (+)-fenfluramine or (+)-norfenfluramine levels were found in the brain of rats treated with devazepide. 5 The effect of CCK-8 on meal size was completely antagonized by 2 mg kg-1 metergoline. A significant interaction was also found between 2 mg kg-1 metergoline and CCK-8 as regards their effect on the inter-meal interval. 6 The results suggest a reciprocal interaction between 5-HT and CCK-8 in enhancing the satiating effect of food in rats.