Stria terminalis lesions attenuate the effects of posttraining naloxone and beta-endorphin on retention

These experiments examined the effect of posttraining administration of naloxone and beta-endorphin in rats with lesions of the stria terminalis (ST). Rats with sham or bilateral ST lesions were trained either in an inhibitory avoidance task or in a Y-maze discrimination task and, immediately after training, received an ip injection of saline, naloxone (0.5, 2.0 or 5.0 mg/kg in the avoidance task; 3.0 mg/kg in the Y-maze task), or beta-endorphin (10.0 micrograms/kg). Retention of each task was tested 24 hr following training. In the Y-maze task, retention was assessed by training on a reversed discrimination. The ST lesions did not affect retention of either task in otherwise untreated animals. However, in both tasks, ST lesions attenuated the memory-enhancing effects of naloxone as well as the memory-impairing effects of beta-endorphin. These findings are consistent with other recent evidence suggesting that the amygdala may be involved in posttraining memory modulation.