Nutrient-conditioned flavor preference and incentive value measured by progressive ratio licking in rats

Rats develop strong preferences for flavors associated with the postingestive actions of glucose and other nutrients. This preference may involve changes in both the hedonic appeal and incentive salience of the nutrient-paired flavor. The present study used a progressive ratio (PR) operant licking task to evaluate the degree to which nutrient conditioning changes the incentive value of flavors. Food restricted rats were trained to associate one flavored saccharin solution (CS+) with intragastric glucose infusions and another flavored solution (CS-) with water infusions. The rats subsequently showed a strong preference for the CS+ in two-bottle tests and also licked more for the CS+ than CS- in PR tests. PR licking for the CS+ was similar to that for an 8% fructose solution. Together with earlier data indicating that the CS- is isopreferred to a 3% fructose solution, these findings indicate that IG glucose conditioning enhances the hedonic and incentive value of the CS+ solution so that the animal responds as if the solution had a sweeter taste.