Learning abilities depend on NMDA-receptor density in hippocampus in adult rats

The hippocampal NMDA-receptor is predominantly involved to establish long-term potentiation (LTP) which is assumed to underlie fundamental molecular mechanisms of learning and memory. In the present study, NMDA-receptor density was investigated in parietotemporal cerebral cortex and in hippocampus of commonly bred naive adult male Wistar rats which had performed well or poorly in the passive avoidance paradigm. NMDA-receptor binding was determined in saturation experiments using (3H) MK-801 as a ligand and data for KD and Bmax were calculated from Scatchard plots. In general, higher NMDA receptor density was found in the hippocampus as compared to parietotemporal cerebral cortex. This regional difference became particularly obvious in good performers but was abolished in poor performers. In the hippocampus, a significantly higher NMDA-receptor density could be found in rats which had performed well in the passive avoidance task as compared to poor performers. In contrast, no such differences could be found in parietotemporal cerebral cortex. The data may indicate that the reduction in hippocampal NMDA-receptor density is of functional importance, for cognitive abilities in both physiological and pathophysiological conditions.