Brainstem lesions and gustatory function: III. The role of the nucleus of the solitary tract and the parabrachial nucleus in retention of a conditioned taste aversion in rats

Bilateral electrolytic lesions of the nucleus of the solitary tract (NST) or ibotenic acid lesions of the pontine parabrachial nuclei (PBN) failed to disrupt retention of a preoperatively acquired conditioned taste aversion (CTA) to 0.3 M alanine. For both sham- and NST-lesioned rats, the CTA persisted following 3 nonreinforced conditioned stimulus (CS) presentations. For PBN-lesioned rats, retention was more labile. The preoperatively acquired CTA was extinguished by the 3rd nonreinforced CS exposure. When assessed postoperatively using a novel CS, NST-lesioned rats acquired a new CTA, although they were rendered anosmic with zinc sulfate (P. S. Grigson, T. Shimura and R. Norgren, 1997). Rats with PBN lesions, however, failed to acquire a second CTA postoperatively. Thus, the PBN is essential for the acquisition of a CTA, but neither of the brainstem gustatory nuclei need be intact for the retention of a preoperatively acquired CTA.