THE N-METHYL-D-ASPARTATE RECEPTOR BLOCKER MK-801 PREVENTS THE FACILITATORY EFFECTS OF NALOXONE AND EPINEPHRINE ON RETENTION OF INHIBITORY AVOIDANCE TASK IN RATS

The aim of this study was to evaluate the interaction between N-methyl -D-aspartate (NMDA) receptors and the adrenergic and opioid systems in the modulation of inhibitory avoidance retention. Rats were trained a nd tested in the step-down inhibitory avoidance task (0.3 mA footshock ). The training-test interval was 24 h. The animals received an i.p. i njection of saline or MK-801 (0.0625 mg/kg) 30 min before training, an d saline, epinephrine (25 mu g/kg), or naloxone (0.4 mg/kg) i.p. immed iately after training. In the saline-pretreated rats, epinephrine and naloxone enhanced memory retention. Pretraining MK-801 prevented the f acilitatory effects of those treatments. The present findings suggest that the facilitation of learning by post-training epinephrine and nal oxone is prevented by the pretraining NMDA receptor blockade.