PROTEIN CHEMICAL CHARACTERIZATION AND IMMUNOCYTOCHEMICAL LOCALIZATIONOF THE NMDA RECEPTOR SUBUNIT NMDA R1

In the rat central nervous system, the mRNA encoding the N-methyl-D-as partate receptor subunit R1 is the most ubiquitously distributed among the cloned subunit mRNAs of this glutamate receptor subtype. The N-me thyl-D-aspartate R1 mRNA is very abundantly expressed and N-methyl-D-a spartate R1 coexpression is necessary for functional expression of all other cloned N-methyl-D-aspartate receptor subunits. Therefore, the R 1 subunit is likely to be an essential component of all known N-methyl -D-aspartate receptors in rat brain. By employing sequence specific po lyclonal antibodies, we demonstrate that rat brain N-methyl-D-aspartat e R1, as well as recombinantly expressed receptor protein, has an appa rent molecular mass of 116 kDa in sodium dodecyl sulfate-polyacrylamid e gel electrophoresis. The receptor protein is heavily glycosylated. I t is specifically localized to the central nervous system, and it coen riches with synaptic membranes upon subcellular fractionation of the c erebral cortex. Chemical cross-linking of synaptic membrane proteins s hows that the N-methyl-D-aspartate R1 protein is part of a receptor pr otein complex with a molecular mass of 730 kDa. By using immunocytoche mical methods, we demonstrate a widespread but distinct distribution o f N-methyl-D-aspartate R1 in neurons of the rat brain, with prominent immunostaining in certain layers of the cerebral cortex, in the hippoc ampus and dentate gyrus, as well as in the cerebellum.