EXPRESSION OF GROUP ONE METABOTROPIC GLUTAMATE-RECEPTOR SUBUNIT MESSENGER-RNAS IN NEUROCHEMICALLY IDENTIFIED NEURONS IN THE RAT NEOSTRIATUM, NEOCORTEX, AND HIPPOCAMPUS

Metabotropic glutamate receptors (mGluRs) can be divided into three gr oups based on sequence homology and pharmacology. We studied expressio n of group I mGluRs (mGluR1 and mGluR5) in identified neurons of the r at neostriatum, neocortex, and hippocampus using in situ hybridization . Tissue sections were hybridized with radiolabeled RNA probes for mGl uR1 or mGluR5 and digoxygenin labeled RNA probes detecting somatostati n (SOM), preproenkephalin (ENK), preprotachykinin (SP), glutamic acid decarboxylase 67 (GAD(67)), parvalbumin (PARV), or choline acetyltrans ferase (ChAT) mRNA. In the striatum, mGluR1 hybridization signal was o bserved in all six neuronal populations. The strongest signal was foun d in SP-positive neurons, with a lower signal in ENK-positive neurons. All striatal interneurons were labeled less intensely than ENK- and S P-positive projection neurons. For striatal mGluR5 mRNA, both SP- and ENK-positive projection neurons were intensely labeled, but only GAD(6 7)-positive interneurons exhibited a significant signal. In the neocor tex and hippocampus, mGluR1 and mGluR5 hybridization signals were stud ied in SOM-, GAD(67)-, and PARV-positive neurons. Hybridization signal for mGluR1 mRNA was intense in SOM-positive neurons of the cortex, CA 1, CA3, and dentate gyrus, and weaker in GAD(67)-positive neurons of C A3 and dentate gyrus. MGluR5 signals were intensely labeled in SOM-, G AD(67)- and PARV-positive neuronal populations of the cortex and hippo campus. SOM-positive neurons were more intensely labeled in the hippoc ampus than cortex.