Systemically administered N-methyl-D-aspartate interferes with acquisition of a passive avoidance response in rats.

The effect of several doses of systemically administered N-methyl-D-aspartate (NMDA) was studied on step-through passive avoidance (PA) retention in rats. Retention of single trial PA was significantly reduced by preacquisition (30 minutes) doses of NMDA (3, 10, 30, and 50 mg/kg SC). Preacquisition amnesia was found when NMDA (30 mg/kg SC) was administered between two and 60 minutes. At shorter and longer pretreatment times (0.5 and 180 minutes) NMDA (30 mg/kg SC) did not disrupt retention testing. Across the same dose range and pretreatment times, NMDA failed to interfere with PA retention when given after acquisition or before retention testing. The results suggest that systemic NMDA administration can interfere with the acquisition of a PA response but does not alter consolidation of information or retrieval.