Forebrain contribution to the induction of a brainstem correlate of conditioned taste aversion: II. Insular (gustatory) cortex

The induction of c-Fos-like immunoreactivity (c-FLI) in the intermediate division of the nucleus of the solitary tract (iNTS) has been shown to be a cellular correlate of the behavioral expression of a conditioned taste aversion (CTA). To further define neuroanatomical structures and pathways that contribute to this cellular response and to CTA learning in general, electrolytic lesions of insular (gustatory) cortex (IC) were combined with immunostaining for c-FLI. Rats were given either unilateral or bilateral electrolytic lesions of insular cortex or `sham' operations. Following surgery, `paired' animals were given a single conditioning trial consisting of intraoral infusion of 5-ml 0.15% sodium–saccharin followed by injection with LiCl (0.15 M, 20 ml/kg, i.p.) while `unpaired' controls received a non-contingent saccharin–LiCl presentation. Rats with bilateral lesions showed no behavioral evidence of having acquired a CTA. Increases in c-FLI in iNTS were evident, but reduced, relative to `sham' animals. Rats with unilateral-lesions displayed a CTA by rejecting the saccharin, although increases in c-FLI on the side of the iNTS ipsilateral to the lesion were reduced relative to that seen in `sham' animals. A comparison of these results with those obtained after amygdala lesions supports the conclusion that amygdala and insular cortex are necessary, but not sufficient, for the behavioral expression of a CTA.