COEXPRESSION OF STRIATAL DOPAMINE-RECEPTOR SUBTYPES AND EXCITATORY AMINO-ACID SUBUNITS

The striatal cellular coexpression patterns for the D-1A and D-2 dopam ine (DA) receptor subtypes and the ionotropic excitatory amino acid (E AA) subunits of the N-methyl-D-aspartate (NMDA-R-1) and the alpha-amin o-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) (GluR(1) and Gl uR(2/3)) receptor subunits were examined morphologically. Their coinci dence was assessed by visualization of mRNA transcripts, localization of encoded receptor proteins, and binding analysis using concurrently paired methods of fluorescence detection. The findings indicated that 1) mRNA transcripts for both receptor systems were detected in the med ium-sized neuron population, and the distribution of receptor message closely reflected protein and binding patterns, with the exception of the GluR(1) subunit; 2) both DA receptor mRNA transcripts were coexpre ssed with each ionotropic EAA receptor subunit examined and with each other, and NMDA and AMPA receptor subunits also showed coincident expr ession; 3) D-1A DA receptor protein was detected in neurons which coex pressed EAA subunit proteins; and 4) GluR(2/3) and NMDA-R-1 subunit pr oteins were coexpressed in medium-sized neurons which also demonstrate d D-2 DA receptor binding sites. These findings suggest morphological receptor ''promiscuity'' since the coexpression patterns between DA an d EAA receptors were found in all permutations. The results provide a spatial framework for physiological findings describing functional int eractions between the two DA receptor types and between specific DA an d EAA receptors in the striatum. (C) 1997 Wiley-Liss, Inc.