Differential distribution of ionotropic glutamate receptor subunits in therat olfactory bulb

The subcellular localization of ionotropic glutamate receptor (GluR) subuni ts was examined with light and electron microscopy in the rat olfactory bul b by using antibodies to alpha-amino-3-hydroxy-5-methylisoxazole-4-propioni c acid (AMPA) receptor subunits: GluR1, GluR2/3, and GluR4; and kainate (KA ) receptor subunits: GluR5/6/7. Immunoreactivity to GluR1 was heavy in the glomerular layer, moderate in the external plexiform layer and localized to periglomerular somata and dendrites, short axon somata and dendrites, mitr al cell somata, and mitral/tufted dendrites. GluR2/3 immunoreactivity was h eavy in the external plexiform and glomerular layers and localized to perig lomerular somata and dendrites, mitral cell somata, mitral/tufted dendrites , granule cell somata, and olfactory nerve-associated glia. GluR4 immunorea ctivity showed heavy staining in the external plexiform and olfactory nerve layers with localization to mitral cells, mitral/tufted dendritic processe s, and olfactory nerve glial processes. GluR5/6/7 immunoreactivity was heav y in the external plexiform layer, moderate in the olfactory nerve and glom erular layers, and localized to granule cells, mitral cells, and mitral/tuf ted dendritic processes. Ultrastructural immunolabeling for all antibodies examined showed immunoreactivity in the postsynaptic membrane and densities , adjacent dendritic cytoplasm, and somatic cytoplasm. These data demonstra te a highly specific laminar, cellular, and subcellular distribution of ion otropic GluR subunits within the primary afferent and local synaptic circui ts of the olfactory bulb. The results are consistent with the notion that t he different roles subserved by glutamate in the olfactory bulb are actuate d, in part, by a differential distribution of GluR subunits. J. Comp. Neuro l. 405:233-246, 1999. (C) 1999 Wiley-Liss, Inc.