Brainstem lesions and gustatory function: II. The role of the nucleus of the solitary tract in Na⁺ appetite, conditioned taste aversion, and conditioned odor aversion in rats

Rats with lesions of the nucleus of the solitary tract (NST) that demonstrated flat concentration-response functions for NaCl and sucrose (T. Shimura, P. S. Grigson, and R. Norgren, 1997) expressed a significant (albeit reduced) salt appetite following sodium depletion, and a normal conditioned taste aversion (CTA) for alanine when paired with lithium chloride-induced toxicosis. Rats with lesions of the NST also could acquire a conditioned odor aversion, but the CTA to alanine was not mediated by odor cues because other rats with NST lesions also demonstrated normal CTA learning even when made anosmic with zinc sulfate. Together, the data suggest that the rostral NST is essential for responding appropriately to increasing concentrations of a tastant, but not for the chemical identification necessary for sodium appetite and CTA learning.