Starch-based conditioned flavor preferences in rats: influence of taste, calories and CS-US delay

Six experiments examined the rat's preference for flavors associated with hydrolysed starch (Polycose) solutions. Hungry rats developed a preference for a flavor (CS+) mixed into a saccharin-sweetened 16% Polycose solution over a flavor (CS-) mixed in saccharin-water. The addition of acarbose, a drug which inhibits starch digestion, to the Polycose solution blocked the flavor preference. This finding indicates that it is the postingestive rather than the taste properties of Polycose that condition flavor preferences. Rats also developed a preference for a CS+ flavor that preceded the ingestion of a Polycose solution by 10 min. This flavor conditioning, however, was not obtained in all experiments. Some CS flavors may be more effective than others in producing conditioned flavor preferences over a delay. Preference conditioning over a delay was facilitated when the rats had previously learned that the taste of the US (Polycose) was not associated with rapid caloric repletion; this was accomplished by giving the rats prior exposure to a Polycose + acarbose solution. Rats with such pre-exposure learned to prefer a CS + flavor that preceded by 10 to 60 min the consumption of a Polycose solution (without acarbose). The results demonstrate that calorie-based flavor preferences can be conditioned over a delay, but conditioning is influenced by the nature of the CS and US stimuli used.