c-Fos induction in the rat nucleus of the solitary tract correlates with the retention and forgetting of a conditioned taste aversion.

Recently, we have described a potential neuronal correlate of the behavioral expression of a conditioned taste aversion (CTA) against sucrose at the level of c-Fos expression. Intraoral infusions of sucrose induce c-Fos-like immunoreactivity (c-FLI) in the intermediate nucleus of the solitary tract (iNTS) after a CTA has been acquired for sucrose. Sucrose infusions do not induce c-FLI in the iNTS of unconditioned rats or in conditioned rats after extinction of the CTA. Here, we describe persistence of altered responsiveness of the iNTS in rats with CTAs against sucrose by intraorally infusing sucrose 2 days, 3 months, or 6 months after acquisition of the CTA. Sucrose infusions induced c-FLI in the iNTS 6 months after conditioning. The behavioral expression of the CTA was attenuated at 6 months but not at 3 months; the number of c-FLI positive cells in the iNTS was proportional to the magnitude of the expression of the CTA. This evidence strengthens our hypothesis that c-FLI in the iNTS is a neuronal correlate of the expression of a CTA.