Pre- or Post-training Administration of the NMDA Receptor Blocker MK-801 Impairs Object Recognition Memory in Rats

The aim of the present study was to investigate the effects of NMDA receptor blockade on formation of object recognition memory. In the first experiment, adult Wistar rats were given an intraperitoneal injection of saline or the NMDA receptor antagonist [(+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclo-hepten-5,10-imine-maleate] (MK-801) (0.001, 0.01, or 0.1 mg/kg) 20 min prior to training in a novel object recognition task. In the second experiment, saline or MK-801 (0.1 mg/kg) were given immediately after training. Memory retention was tested 1.5 and 24 h after training. MK-801 impaired both short- and long-term retention of object recognition memory when given either before or after training. The results suggest that NMDA receptor activation is necessary for formation of object recognition memory.