Methylphenidate, amygdalectomy, and active avoidance performance in the rat

Amygdalectomized and control rats were given 400 active avoidance training trials in a shuttle box. Control animals received 0, 4, 8, or 16 mg/kg of methylphenidate throughout acquisition. Amygdalectomized animals were given the first 200 trials without drug, followed by 200 trials with drug. The administration of methylphenidate produced an abrupt and large improvement in performance in the amygdalectomized animals. One month after acquisition under the drug, retraining without drug revealed a significant retention effect for the three amygdaloid-drug groups relative to the nondrug-amygdaloid group. These results indicate that although amygdalectomy impairs the performance of avoidance responses, it does not prevent the learning or retention of such responses. Since methylphenidate appears to act primarily on dopaminergic mechanisms, the possible influence of amygdalectomy on such mechanisms is discussed.