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-asp artate (NMDA) receptors in the enhancement of retention caused by a se cond 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 st ep-down inhibitory avoidance task (24 h interval between sessions). Th e 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 retent ion caused by additional training when given 30 min before, but not im mediately after, the second training session. A control experiment sho wed that the effect was not due to analgesia. We may conclude that NMD A receptors are critical for the acquisition and enhancement of retent ion of an inhibitory avoidance task.