Conditioned changes in appetitive and consummatory responses to flavors paired with oral or nutrient reinforcement among adult rats

Recent studies of the behavioral organization of conditioned flavor prefere nces have suggested the involvement of at least two separate learning syste ms-an appetitive response system sensitive to the oral hedonic properties o f the reinforcer, and a consummatory response system sensitive to its nutri ent properties. However, these prior studies were conducted with weanling r ats, that differ from adults in terms of their prior experience with food, their learning competencies, and the peculiar ontogenetic constraints on th eir behavior. It is, therefore, unknown whether flavor preference behaviors are similarly organized in adult rats. In this experiment, adult rats were trained to associate a specific CS flavor with either the sweet taste or t he postingestive nutrient effects of sucrose. Conditioned appetitive orient ing and consummatory oral responding to the CS flavors were then measured. Unlike weanling rats, adult rats exhibited both conditioned appetitive beha vior and conditioned consummatory behavior in response a CS that was previo usly paired with either oral hedonic or nutrient reinforcement. These resul ts suggest a set of important developmental changes in the neurobehavioral mechanisms of flavor preference learning in the postweaning period. (C) 200 0 Elsevier Science Inc. All rights reserved.