Differential effects of postingestive feedback on the reward value of sucrose and lateral hypothalamic stimulation in rats.

The effects of postingestive feedback on the value of intraoral sucrose and lateral hypothalamic (LH) stimulation were compared. Rats chose between a fixed LH stimulation train or a compound reward composed of the same stimulation train and an oral infusion of 1 M sucrose. The rats preferred the compound reward when postingestive feedback was reduced by opening a gastric cannula. However, when the cannula was closed, the compound was preferred only at the beginning of each session, and preference declined or reversed as consumption continued. A second experiment showed that the reduction in preference caused by closing the gastric cannula was not due to a punishing effect of the gastrointestinal load. This study suggests that postingestive signals modulate gustatory reward at a stage of processing before gustatory and brain stimulation rewards are combined.