Flavor preferences conditioned by intragastric nutrient infusions in food restricted and free-feeding rats

The role of deprivation state in flavor preference conditioning by nutrients was investigated in rats fitted with intragastric (IG) catheters. In different experiments, food restricted (FR) and food ad libitum (AL) groups were trained to drink one flavored solution (CS+) paired with IG infusions of maltodextrin, corn oil, or casein and another flavored solution (CS-) paired with IG water infusions. Training intakes of the CS solutions were limited to equate the exposure of the FR and AL groups. The IG nutrient infusions conditioned flavor preferences in FR and AL groups which, in three of four experiments, were of similar magnitude. Food restriction did, however, increase the overall intake of the CS+ solutions during testing. Rats trained with one CS+ while food restricted and a second CS+ while food unrestricted showed similar preferences for the two CS+ flavors. Prefeeding AL rats to satiety with chow prior to daily training sessions did not prevent them from developing a preference for a CS+ paired with IG maltodextrin. These findings indicate that the postoral actions of nutrients are reinforcing in food sated as well as hungry rats.