Changes in behavior of hippocampal-lesioned rats across a 6-week postoperative period

Abstract

The postoperative behavior of rats with one-stage bilateral lesions of the dorso-lateral hippocampus was examined preoperatively and on 15 separate occasions over a 42-day postoperative period. Repeated measures of spontaneous alternation in a T-maze and general activity in an open field were made. The postoperative behavior of the hippocampal-lesioned rats was compared with that of control rats which had sustained one-stage bilateral lesions of the neopallium overlying the hippocampal formation. The effect of the neopallial lesion on both behaviors was transitory; preoperative levels of behavior returned within 72 h postoperatively. For the hippocampal-lesioned group there was a drop in the level of spontaneous alternation on Day 2 postoperatively, a brief return to preoperative levels on Day 3, and then a sustained depression in rate until Day 14, when a return toward preoperative alternation rates occurred. In the open field, the hippocampal-lesioned subjects displayed a 3-4-day period of hypoactivity, followed abruptly by a 7-9-day period of hyperactivity. These subjects then returned to preoperative levels of activity. The nature and time course of these shifts in postoperative behavior were discussed in terms of their possible relationship to findings regarding synaptic reinnervation of the septal nuclei.