LOCALIZATION OF MGLUR1A-LIKE IMMUNOREACTIVITY AND MGLUR5-LIKE IMMUNOREACTIVITY IN IDENTIFIED POPULATIONS OF STRIATAL NEURONS

Metabotropic glutamate receptors are important mediators of excitatory amino acid neurotransmission in the striatum. Two-color immunofluores cence histochemistry and immunohistochemistry in combination with retr ograde tract-tracing techniques were used to examine the distribution of metabotropic glutamate receptor subtypes 1a and 5 (mGluR1a and mGlu R5) among identified subpopulations of striatal projection neurons and interneurons. The majority of striatopallidal and striatonigral neuro ns were double-labeled for both mGluR1a or mGluR5. Approximately 60% t o 70% of either striatonigral or striatopallidal neurons expressed mGl uR1a- or mGluR5-like immunoreactivity. The percentage of double-labele d striatopallidal or striatonigral projection neurons did not differ a mong striatal quadrants. Striatal interneurons expressing parvalbumin or somatostatin or choline acetyltransferase exhibited varying degrees of expression of mGluR1a or mGluR5. Virtually all (94%) parvalbumin-i mmunoreactive striatal neurons expressed mGluR1a-like immunoreactivity with a majority (79%) of these neurons expressing mGluR5-like immunor eactivity. A high percentage (89%) of striatal choline acetyltransfera se-immunoreactive neurons were double-labeled for mGluR1a-like immunor eactivity. Approximately 65% of striatal choline acetyltransferase-imm unoreactive neurons expressed mGluR5-like immunoreactivity. A majority (65%) of somatostatin-immunoreactive striatal interneurons expressed mGluR1a-like immunoreactivity with a slightly lower percentage (55%) e xpressing mGluR5-like immunoreactivity. These findings indicate consid erable heterogeneity among striatal projection and interneurons with r espect to mGluR1a and mGluR5 expression. There may be subpopulations o f striatonigral and striatopallidal projection neurons. These results are consistent as well with prior data indicating subpopulations of th e different classes of striatal interneurons. (C) 1998 Elsevier Scienc e B.V.