The Effect of Experimentally Induced Focal Epilepsy on Operant Responding in the Rat

Dose-response studies were performed on freely moving rats bearing chronically implanted electrodes. The effects of intracortical injections of penicillin, bicuculline, and conjugated estrogens (Premarin®) were determined on EEG activity and motor performance. Bicuculline in doses of 0.025 and 0.05% regularly produced spike and afterdischarge (AD) patterns of rapid onset (<10 sec), brief duration (<20 min), and marked intensity. Lower doses had little or no effect. Premarin 1% and penicillin 100 international units produced spike and AD patterns of slower onset (5 min), longer duration (up to 2 hr), and mild intensity. Smaller doses generally produced no AD activity, whereas larger doses produced epileptic patterns severe enough to preclude their use in operant studies. Penicillin and Premarin both produced a significant decrease in operant-response rate in animals trained to bar press on a FR 20 schedule. A marked variability was noted in the behavioral responses of individual rats to the disruptive effects of the epileptogens.