THE DISTRIBUTION OF GLUTAMATE RECEPTORS IN CULTURED RAT HIPPOCAMPAL-NEURONS - POSTSYNAPTIC CLUSTERING OF AMPA-SELECTIVE SUBUNITS

The distribution of several glutamate receptor subunits was investigat ed in cultured rat hippocampal neurons by in situ hybridization and im munocytochemistry. The AMPA/kainate-selective receptors GluR1-6 exhibi ted two patterns of mRNA expression: most neurons expressed GluR1, R2, and R6, whereas only about 20% expressed significant levels of GluR3, R4, and R5. By immunocytochemistry, the metabotropic glutamate recept or mGluR1alpha was detectable only in a subpopulation of GABAergic int erneurons. GluR1 and GluR2/3 segregated to the somatodendritic domain within the first week in culture, even in the absence of synaptogenesi s. Glutamate receptor-enriched spines developed later and were present only on presumptive pyramidal cells, not on GABAergic interneurons. C lusters of GluR1 and GluR2/3 completely colocalized and were restricte d to a subset of postsynaptic sites. Thus, glutamate receptor subunits exhibit both a cell type-specific expression and a selective subcellu lar localization.