c-Fos induction in the rat nucleus of the solitary tract by intraoral quinine infusion depends on prior contingent pairing of quinine and lithium chloride.

Intraoral infusions of sucrose or saccharin induce c-Fos-like immunoreactivity (c-FLI) in the intermediate nucleus of the solitary tract (iNTS) of rats after acquisition of a conditioned taste aversion (CTA). The induction of c-FLI in the iNTS may be a consequence of the shift in behavioral response from ingestive to aversive behaviors that characterize acquisition and expression of a CTA. To test this hypothesis, rats were intraorally infused with 0.3 mM quinine sulfate, an aversive taste, 1. prior to conditioning, 2. after 3 noncontingent (unpaired) infusions of quinine and toxic lithium chloride (LiCl) injections, 3. after conditioning with 3 contingent pairings of quinine and LiCl, and 4. after extinction with repeated unpaired infusions of quinine. Intraoral infusions of quinine induced c-FLI in the iNTS only after acquisition of a CTA against quinine; quinine failed to induce c-FLI in the iNTS of unconditioned, noncontingently treated, or extinguished rats. The pattern of c-FLI in the iNTS induced by expression of a CTA against quinine was quantitatively and anatomically similar to that elicited by sucrose in rats expressing a CTA against sucrose. We conclude that aversive responses per se are not sufficient to induce c-FLI in the iNTS. Furthermore, contingent pairing of quinine and LiCl does not cause a shift in behavioral response from palatable, ingestive behaviors to aversive behaviors as in acquisition of a CTA against sucrose. Thus, we also conclude that a shift in behavior from ingestive to aversive responses is not required for increased c-FLI expression in the iNTS during CTA expression. Therefore, the induction of c-FLI in the iNTS during expression of a CTA may be correlated with neuronal processes specific to acquisition and expression of a CTA.