Cholecystokinin interacts with prefeeding to impair runway performance

Previous experiments demonstrated the ineffectiveness of the C-terminal octapeptide of cholecystokinin (CCK-8) for impairing runway performance by food-deprived rats. These results were consistent with the proposal that CCK-8 does not reduce food intake by inhibiting appetitive motivation but instead acts late in the meal to prematurely trigger satiety. For further evaluation of this hypothesis, the effect of CCK-8 on runway performance was assessed after 21 h food-deprived rats consumed a partial meal of 30% sucrose. Injection of 1.0 micrograms/kg CCK-8 after rats were allowed 3 min (6.2 ml consumed) or 5 min (9.7 ml) access to 30% sucrose produced significant reductions in running speed of 43% and 70%, respectively. After 5 min prefeeding, 0.25 and 0.50 micrograms/kg CCK-8 also produced significant decreases in speed of 20% and 59%, respectively. By contrast, CCK-8 had little or no effect without prefeeding. Doses of 0.25 and 0.50 micrograms/kg failed to affect running speed on these tests and 1.0 micrograms/kg produced a small (7%) though significant decrease. These results suggest that inhibition of feeding motivation after CCK-8 administration develops during the course of the meal through interaction with signals generated by the ingestion of food.