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

Abstract

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 and 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. injection of saline or MK-801 (0.0625 mg/kg) 30 min before training, and saline, epinephrine (25 μg/kg), or naloxone (0.4 mg/kg) i.p. immediately after training. In the saline-pretreated rats, epinephrine and naloxone enhanced memory retention. Pretraining MK-801 prevented the facilitatory effects of those treatments. The present findings suggest that the facilitation of learning by post-training epinephrine and naloxone is prevented by the pretraining NMDA receptor blockade.