Cholecystokinin conditions flavor preferences in rats

The present study investigated whether cholecystokinin (CCK), an intestinal hormone that is a putative satiety agent, can condition flavor preference in rats. In experiment 1 food-deprived rats were trained to consume two different-flavored saccharin solutions in separate one-bottle tests. One flavor (the CS+) was paired with intraperitoneal injections of CCK octapeptide (0.125-4 micrograms/kg); the other flavor was paired with intraperitoneal injections of saline. Flavor preferences were then assessed in subsequent two-bottle choice tests. The 0.125 and 0.25 micrograms/kg doses failed to suppress CS+ intake or produce flavor preferences. CCK at 0.5 micrograms/kg did not reliably suppress CS+ intake in the one-bottle tests but produced a reliable preference for the CS+ in the two-bottle tests; percent CS+ intakes ranged from 50 to 62% in the four preference tests. At 1 microgram/kg, CCK suppressed CS+ intake and produced a marginal preference for the CS+. The 2 micrograms/kg dose suppressed CS+ intake but failed to condition a CS+ preference. The 4 micrograms/kg dose of CCK produced a potent suppression of CS+ intake and a strong aversion to that flavor. The preference conditioning effect of CCK at 0.5 microgram/kg was replicated in a second experiment using flavored Polycose solutions. The finding that low doses of CCK condition flavor preferences in rats is compatible with the hypothesis that endogenous CCK can mediate satiety and further suggests a role for CCK in learned food preferences. The aversion conditioned by the highest dose of CCK does not detract from this interpretation, since food, if consumed in excess, can also have aversive consequences.