Epileptiform lesions in rat hippocampus and acquisition of two-way avoidance

Three experiments were conducted to examine the effects on the acquisition of two-way active avoidance of implantation into the hippocampus of rats of two substances (aluminum hydroxide, penicillin) known to produce epileptogenic electrical discharges. In Experiment 1 bilateral deposits of aluminum hydroxide (ALOH) were placed in the hippocampus and the effects of this manipulation were compared to the effects of bilateral hippocampal aspiration. Sufficient postoperative time (130 days) was allowed such that epileptogenic discharges developed in the ALOH-implanted rats. Both bilateral hippocampal-ALOH deposits and bilateral hippocampal aspiration resulted in facilitated acquisition of the two-way avoidance. The results of Experiment 2 replicated this observation, but also indicated that bilateral hippocampal deposits of penicillin did not cause detectable effects on acquisition of the avoidance. Epileptiform activity produced by the penicillin was observed to disappear by postoperative Day 4. In Experiment 3 unilateral hippocampal aspiration was combined with contralateral implants of either ALOH or penicillin and avoidance training was begun 13 days postoperatively. Epileptiform activity was not observed in the ALOH-implanted rats and disappeared by postoperative Day 4 in the penicillin implanted rats. No significant changes were observed in the rate of acquisition of two-way active avoidance as a result of the manipulations done in Experiment 3. It is concluded that epileptiform discharge initiated focally within the hippocampus produces effects on the acquisition of two-way active avoidance which are similar to the effects produced by bilateral ablation.