REGIONAL, CELLULAR, AND ULTRASTRUCTURAL DISTRIBUTION OF N-METHYL-D-ASPARTATE RECEPTOR SUBUNIT-1 IN MONKEY HIPPOCAMPUS

The regional, cellular, and subcellular distributions of N-methyl-D-as partate (NMDA) receptor subunit 1, NMDAR-1, were investigated in monke y hippocampus by using a monoclonal antibody directed against a fusion protein corresponding to aa 660-811 of NMDAR-1. The data indicate tha t many neurons in each subfield of the hippocampus contain NMDAR-1 pro tein, although the intensity and distribution of immunoreactivity vari ed across regions, strata, and cellular compartments. In stratum lucid um of CA3, messy fiber axons were immunoreactive for NMDAR-1, which ma y correspond to previously hypothesized presynaptic receptors. NMDAR-1 -labeled postsynaptic profiles were present in stratum radiatum of CA3 but were largely absent from stratum lucidum. Such intraneuronal segr egation of glutamate receptor subunits or classes may be spatially cor related with afferent systems that exhibit laminar segregation and ter minate in different portions of the postsynaptic dendritic tree. For e xample, in CA3 pyramidal cells, NMDA receptors are postsynaptic in dis tal apical dendrites (stratum radiatum), where NMDA-dependent longterm potentiation in rats is mediated by associational/commissural afferen ts, and are absent from proximal apical dendrites (stratum lucidum), w here NMDA-independent longterm potentiation is mediated by the messy f iber input.