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In this study, we investigated the effects of both N-methyl D-aspartate (NMDA) and MK-801 on WIN55,212-2(WIN)-induced amnesia in rats. Step-through inhibitory avoidance of memory was used to examine the retrieval of memory, 24 h after training. All drugs were injected bilaterally into the dorsal hippocampus (intra-CA1) of rats. Pretraining and posttraining or pretesting administration of the nonselective CB1/CB2 receptor agonist, WIN (0.5 µg/rat), decreased the step-through latency. However, amnesia induced by pretraining or posttraining injections of WIN was reversed by a pretest administration of WIN (0.25 and 0.5 µg/rat). Pretest microinjections of different doses of NMDA (0.1, 0.5, and 1 µg/rat) elicited no response, but NMDA (0.5 and 1 µg/rat) did induce full recovery from amnesia induced by WIN (0.5 µg/rat). The posttraining and pretest injection of a higher dose of the NMDA receptor antagonist, MK801 (MK; 4 µg/rat), caused an impairment in the memory retrieval. However, amnesia induced by posttraining injections of MK (4 µg/rat) was reversed by a pretest administration of MK (4 µg/rat). In addition, pretest administration of different doses of the antagonist (2 and 4 µg/rat) induced full recovery of WIN-induced amnesia, but did not influence memory recovery in the subjects, which had received posttraining (0.5 µg/rat) and pretest WIN (0.25 and 0.5 µg/rat). Pretesting coadministration of ineffective doses of WIN (0.1 µg/rat) with NMDA (0.1 µg/rat), but not with MK (1 µg/rat), restored WIN-induced (0.5 µg/rat) amnesia. It can be concluded that the NMDA receptor mechanism located in the dorsal hippocampus may be involved in WIN-induced amnesia.

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