Hippocampal lesion effects on conditioned taste aversion and pituitary-adrenal activity in rats.

A series of experiments examined the effects of hippocampal lesions on conditioned taste aversion (CTA) and pituitary-adrenal activity. Experiment 1 examined recovery from a conditioned taste aversion under conditions of free extinction. Hippocampal and unoperated rats recovered from the aversion at the same rate. Further, this experiment showed that the suppression in drinking in both groups produced by lithium chloride (LiCl) injection was a conditioned taste aversion (was dependent upon the pairing of the taste stimulus with LiCl) and not enhanced neophobia. In Experiment 2 there were no behavioral effects of the lesion in a forced extinction CTA paradigm. In addition, hippocampal lesions failed to alter pituitary-adrenal responsiveness to LiCl. In the same experiment, pituitary-adrenal responsiveness of hippocampectomized rats, when re-exposed to the taste paired earlier with LiCl, was altered. Hippocampal lesions eliminated the elevation in corticosterone shown by unoperated control and neocortical-lesioned rats. The third experiment replicated this finding showing again that hippocampal-lesioned rats failed to show the forced extinction elevation in corticosterone when exposed to the aversive taste (Experiment 3). These data were integrated with other reports of behavioral and pituitary-adrenal alterations in hippocampal-lesioned rats.