EFFECTS OF SUCCESSIVE BILATERAL HIPPOCAMPECTOMY ON DRL-20 PERFORMANCE IN RATS

The effects of single-stage vs. two-stage, successive bilateral hippocampectomy on acquisition of a DRL [differential reinforcement low rate] 20 operant schedule were determined. Rats received training on a continuous reinforcement operant schedule prior to either single-stage total hippocampectomy, sham operative treatment or bilateral lesion of either dorsolateral or posteroventral hippocampus. After 40 days of DRL 20 training, the seriatim groups received bilateral lesions of remaining hippocampal tissue. All animals then received 15 final days of DRL 20 training. The single-stage lesion group was significantly less efficient than the sham operates. During interoperative training the 2 seriatim groups were equally efficient and did not differ from the sham operates. After the 2nd serial lesion, the group that had received an initial lesion of the posteroventral hippocampus decreased DRL performance to a level equal to that of the single-stage group while the group which had initially received anterodorsal lesions maintained efficient DRL performance.