Blockade of NMDA receptors pre-training, but not post-training, impairs object displacement learning in the rat.

Several forms of hippocampal-dependent learning rely upon activation of the N-methyl-d-aspartate (NMDA) subtype of glutamate receptor. Here we have investigated the effects of administration of the NMDA receptor antagonist (+/-)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) on the performance of rats in an object displacement task and the possible role of extracellular signal-regulated kinase (ERK) in this form of learning. The data show that rats injected intraperitoneally with CPP (10 mg/kg) before, but not after, training in the object displacement task displayed impairments in spatial learning when compared with saline-injected controls.