NMDA depolarizations and long-term potentiation are reduced in the aged rat neocortex.

N-Methyl-D-aspartate (NMDA) responses were recorded intracellularly in layer V neocortical neurons in in vitro slices taken from young (4-6 months) and aged (27-29 months) Fischer 344 rats. Increasing amounts of NMDA produced membrane depolarizations in both groups of cells. The regression analysis showed significantly reduced sensitivity to NMDA in old neurons compared to young. A significant long-term potentiation of the field potential evoked by subcortical white matter stimulation was present in young but not in old slices. These results suggest that aging results in a decreased sensitivity to NMDA and impaired synaptic plasticity in the neocortex.