Abstract
When animals drink a taste solution (conditioned stimulus, CS) and are followed by malaise (unconditioned stimulus, US), the animals acquire aversion to the taste solution. This is a kind of fear learning referred to as conditioned taste aversion (CTA). Palatability shifts from ingestive to aversive occur after the acquisition of CTA. Recently, we found that the GABAergic system in the ventral pallidum, a part of reward system, is involved in taste palatability. To elucidate the role of the VP on the expression of CTA, we examined the effects of microinjections of a GABAA receptor antagonist, bicuculline, on the intake of CS in the retrieval test. Rats received a pairing of palatable saccharin (CS) with an i.p. injection of 0.15 M lithium chloride (US). After this conditioning, vehicle or bicuculline (50, 100 or 200 ng) was bilaterally infused into the VP immediately before the re-exposure to saccharin solution. The microinjections of bicuculline significantly increased the saccharin intake. However, when the rats acquired aversion to innately aversive quinine hydrochloride (QHCl) as the CS, the microinjections of bicuculline had no effects on the intake of QHCl. These results may be explained by our previous finding that the blockade of the GABAergic transmission in the VP increases the intake of sweet solution. [Jpn J Physiol 55 Suppl:S201 (2005)]
