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

Abstract

Metabotropic glutamate receptors (mGluRs) in the medulla oblongata have been suggested to be involved in the regulation of autonomic function. The aim of the present study was to examine the localization and expression of four 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 subtypes studied were differentially distributed in distinct subnuclei in the nucleus of the solitary tract (NTS). mGluR1a immunoreactivity was identified in cell bodies, dendrites, and axonal processes in the intermediate, dorsal lateral, and interstitial subnuclei of the NTS. No mGluR1a immunoreactivity was observed in the commissural or medial NTS subnuclei. Immunoreactivity for mGluR2/3 and mGluR5 as observed in fibers and putative axonal processes in the interstitial, intermediate, and dorsolateral subnuclei of the NTS. In contrast, mGluR7 was expressed primarily in fibers and terminals in the central and commissural NTS subnuclei. Expression of mGluR2/3 was clearly evident in cell bodies, dendrites, and axonal processes within the area postrema. The vagal outflow nuclei were also studied. The dorsal motor nucleus of the vagus (DMN) contained mGluR1a cell bodies, dendrites, and axonal fibers and light mGluR2/3 processes. Throughout the rostral‐caudal extent of the compact and semicompact formation nucleus ambiguus, mGluR1a was found in cell bodies and fibers. Within the caudal and rostral regions of the ventral lateral medulla, mGluR1a was observed in cell bodies and fibers. Cell bodies containing mGluR1a were found adjacent to cells staining positive for tyrosine hydroxylase (TH) in these regions but were not colocalized with the TH staining. However, mGluR1a‐expressing neurons in the ventral lateral medulla did appear to receive innervation from TH‐containing fibers. These results suggest that the mGluR1a‐expressing neurons within the ventral lateral medulla are predominantly not catecholaminergic but may be innervated by catecholamine‐containing fibers. These data are the first to provide a mapping of the different mGluR subtypes within the medulla and may facilitate predictions regarding the function of L‐glutamate neurotransmission in these regions. J. Comp. Neurol. 403:486–501, 1999. © 1999 Wiley‐Liss, Inc.

Expression of Group I metabotropic glutamate receptors on phenotypically different cells within the nucleus of the solitary tract in the rat

“…Similar to previous studies (Hay et al, 1999), our data indicate that Group I mGluRs are expressed throughout the NTS. The greatest expression was at the level of and rostral to the AP.…”

“…Fast-acting ionotropic glutamate receptors within the NTS are required for normal baroreflex function (Andresen and Kunze, 1994; Gordon and Sved, 2002; Talman et al, 1980). Metabotropic glutamate receptors (mGluRs) also are present in the NTS (Hoang and Hay, 2001; Chen et al, 2002; Hay et al, 1999) and may influence cardiovascular regulation (Foley et al, 1998, 1999; Viard and Sapru, 2002; Chen et al, 2002; Sekizawa and Bonham, 2006; Liu et al, 1998). Blockade of the sympathoinhibition and depressor response due to microinjection of glutamate into the NTS requires antagonism of both ionotropic glutamate receptors and mGluRs (Pawloski-Dahm and Gordon, 1992; Foley et al, 1998, 1999).…”

Plasticity of vagal brainstem circuits in the control of gastric function

“…Activation of ionotropic glutamate receptors (i.e., NMDA and non-NMDA receptors) is crucial in the transmission of visceral sensory information but several metabotropic glutamate receptors (mGluR) have also been identified within the DVC 48. The mGluR present in the DVC include group II and group III mGluR that are located predominately at presynaptic sites and are negatively coupled to adenylate cyclase.…”

“…The mGluR present in the DVC include group II and group III mGluR that are located predominately at presynaptic sites and are negatively coupled to adenylate cyclase. Their metabotropic nature implies that glutamate can exert long-lasting effects on sensory integration and synaptic transmission 15, 48-54 and, by consequence, could play important roles in the regulation of cAMP levels and modulation of synaptic transmission in GABAergic NTS terminals. In fact, ongoing activation of group II, but not group III, mGluR appears critical in regulating cAMP levels within GABAergic NTS terminals 55.…”

Role of metabotropic glutamate receptors in the regulation of pancreatic functions

“…These observations raise the possibility that a similar distribution pattern may be present in the DMV and that expression of group III mGluRs may be limited to terminals impinging on DMV neurons of a specific phenotype. Furthermore, DMV neurons display mGluR1a immunoreactivity [48], however, the role of these receptors in modulation of pancreatic functions has not been investigated yet.…”