Heterogeneity of metabotropic glutamate receptors in autonomic cell groupsof the medulla oblongata of the rat

Metabotropic glutamate receptors (mGluRs) in the medulla oblongata have bee n suggested to be involved in the regulation of autonomic function. The aim of the present study was to examine the localization and expression of fou r types of mGluRs: mGluR1a, mGluR2/3, mGluR5, and mGluR7: in the dorsal and ventral autonomic nuclei of the medulla of the rat. The four mGluR subtype s studied were differentially distributed in distinct subnuclei in the nucl eus of the solitary tract (NTS). mGluR1a immunoreactivity was identified in cell bodies, dendrites, and axonal processes in the intermediate, dorsal l ateral, and interstitial subnuclei of the NTS. No mGluR1a immunoreactivity was observed in the commissural or medial NTS subnuclei. Immunoreactivity f or mGluR2/3 and mGluR5 as observed in fibers and putative axonal processes in the interstitial, intermediate, and dorsolateral subnuclei of the NTS. I n contrast, mGluR7 was expressed primarily in fibers and terminals in the c entral and commissural NTS subnuclei. Expression of mGluR2/3 was clearly ev ident in cell bodies, dendrites, and axonal processes within the area postr ema. The vagal outflow nuclei were also studied. The dorsal motor nucleus o f the vagus (DMN) contained mGluR1a cell bodies, dendrites, and axonal fibe rs and Light mGluR2/3 processes. Throughout the rostral-caudal extent of th e compact and semicompact formation nucleus ambiguus, mGluR1a was found in cell bodies and fibers. Within the caudal and rostral regions of the ventra l lateral medulla, mGluR1a was observed in cell bodies and fibers. Cell bod ies containing mGluR1a were found adjacent to cells staining positive for t yrosine hydroxylase (TH) in these regions but were not colocalized with the TH staining. However, mGluR1a-expressing neurons in the ventral lateral me dulla did appear to receive innervation from TH-containing fibers. These re sults suggest that the mGluR1a-expressing neurons within the ventral latera l medulla are predominantly not catecholaminergic but may be innervated by catecholamine-containing fibers. These data are the first to provide a mapp ing of the different mGluR subtypes within the medulla and may facilitate p redictions regarding the function of L-glutamate neurotransmission in these regions. (C) 1999 Wiley-Liss, Inc.