The role of gastric and postgastric sites in glucose-conditioned flavor preferences in rats.

Two experiments examined the role of gastric and postgastric contributions in the development of flavor preferences in rats. During training trials, food-deprived rats consumed, on alternate days, a cue flavor paired with glucose infusions and another flavor paired with water infusions. Preferences were assessed in choice tests between the two cue flavors without infusions. The first experiment compared preferences conditioned to a flavor paired with intraduodenal (ID) glucose infusions to those paired with intragastric (IG) infusions. ID glucose-conditioned preferences were as strong as that of IG glucose. The second experiment examined whether the actions of glucose in the stomach alone were sufficient to condition flavor preferences. Glucose infusions were restricted to the stomach with an inflated pyloric cuff and then removed at the end of 30-min training sessions before the cuff was deflated. Rats trained with this procedure did not develop a reliable flavor preference. Flavor preferences were obtained, however, when the cuff was inflated for 30 min after the end of the daily training sessions, or when the cuff was inflated during the training sessions but then deflated without removing the infused glucose. Both of these procedures allowed at least some of the infused glucose to empty into the intestine. Taken together, the results indicate that information from the stomach is neither necessary nor sufficient to produce glucose-conditioned flavor preferences. Such preferences are reinforced by the intestinal and/or postabsorptive actions of glucose.