BRAIN-STEM LESIONS AND GUSTATORY FUNCTION .3. THE ROLE OF THE NUCLEUSOF 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 (N ST) or ibotenic acid lesions of the pontine parabrachial nuclei (PBN) failed to disrupt retention of a preoperatively acquired conditioned t aste aversion (CTA) to 0.3 hi alanine. For both sham- and NST-lesioned rats, the CTA persisted following 3 nonreinforced conditioned stimulu s (CS) presentations. For PBN-lesioned rats, retention was more labile . The preoperatively acquired CTA was extinguished by the 3rd nonreinf orced 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, & R. Norgren, 1997). Ra ts with PBN lesions, however, failed to acquire a second CTA postopera tively. Thus, the PBN is essential far the acquisition of a CTA, but n either of the brainstem gustatory nuclei need be intact for the retent ion of a preoperatively acquired CTA.