Amygdala lesions block the amnestic effects of diazepam

This experiment examined the effects of pre-training systemic injections of the benzodiazepine (BZ) diazepam (DZP) on learning and retention of an inhibitory avoidance response in rats with bilateral lesions of the amygdaloid complex (AC) induced by intra-amygdala injections of the excitotoxin N-methyl-D-aspartic acid (NMDA). Unoperated, sham-operated and AC-lesioned rats received i.p. injections of DZP (1.0 or 2.0 mg/kg) or vehicle 30 min prior to training in a continuous multiple-trial inhibitory avoidance task. Retention was tested 48 h later. The acquisition and retention of the AC-lesioned rats were impaired, relative to that of the unoperated and sham controls. In the unoperated and sham controls, DZP impaired retention but did not affect acquisition. In contrast, in animals with AC lesions, DZP did not affect either acquisition or retention. These findings suggest that the amnestic effects of DZP are mediated, at least in part, through influences involving the AC.