The NMDA receptor blocker MK-801 inhibits the effect of additional training on retention of an inhibitory avoidance task in rats

The aim of this research was to investigate the role of N-methyl-D-aspartate (NMDA) receptors in the enhancement of retention caused by a second training session in inhibitory avoidance task. Female Wistar rats were submitted to a training session only (0.4 mA footshock) or two (0.2 mA footshock) training sessions followed by a test session in a step-down inhibitory avoidance task (24 h interval between sessions). The NMDA receptor blocker dizocilpine (MK-801) (0.0625 mg kg(-1), i.p.) impaired retention when given 30 min before, but not immediately after, the only training session. It also blocked the enhancement of retention caused by additional training when given 30 min before, but not immediately after, the second training session. A control experiment showed that the effect was not due to analgesia. We may conclude that NMDA receptors are critical for the acquisition and enhancement of retention of an inhibitory avoidance task.