Adrenocortical response to novelty stress in rats with dentate gyrus lesions.

Male rats exposed to a novel environment exhibited a marked rise of plasma corticosterone in response to the initial exposure. These animals showed a significant but not complete habituation of their adrenal response after 18 exposures. Following their first exposure to a novel environment, animals with bilateral lesions in the dentate gyrus of the hippocampus had plasma corticosterone concentrations which were significantly lower than those observed for the control animals. Whereas the control groups demonstrated a significant decrease in their adrenal response following 18 exposures (habituation), there was no decrease of the adrenocortical response to novelty stress within the dentate-lesioned group between trials 1 and 18. The effect of the dentate lesions appeared to be specific to the behavioral stress: dentate lesions failed to alter resting levels, or the animal's adrenal responses to laparotomy stress and ether inhalation.