The role of the ventral pallidum GABAergic system in conditioned taste aversion: effects of microinjections of a GABAA receptor antagonist on taste palatability of a conditioned stimulus.

When subjects receive a taste stimulus (conditioned stimulus, CS) that is paired with malaise, they acquire conditioned taste aversion (CTA). It is thought that the taste CS changes from appetitive to aversive after acquisition of CTA. Previous studies have suggested that the ventral pallidum (VP) is involved in the hedonics of taste stimuli, therefore the present study investigated whether the VP is a neural substrate for the shift in preference of the CS after CTA acquisition. In the first experiment, CTA-learned rats received microinjections of the GABA(A) receptor antagonist bicuculline into the VP just before presentation of the CS (saccharin or quinine) in a single-bottle test. The bicuculline-injected rats showed higher intake of the saccharin CS than the vehicle-injected rats. To test whether these results were due to a change in taste preference for the CS, in the second experiment, we examined the effects of bicuculline on the affective aspects of the saccharin CS using a taste reactivity test, which is a useful tool for evaluating taste palatability. The bicuculline-injected rats showed higher appetitive and lower aversive responses to the saccharin CS than the vehicle-injected group. These results suggest that the higher saccharin intake observed in the first experiment was at least partly due to the bicuculline injection, which changed the perceived palatability of the taste CS (saccharin) from aversive to appetitive. The GABAergic system in the VP may play an important role in hedonic-based ingestive behaviors after CTA.