Expression of ionotropic glutamate receptor subunit mRNAs in the hypothalamic paraventricular nucleus of the rat

The hypopthalamic paraventricular nucleus (PVN) coordinates multiple aspect s of homeostatic regulation, including pituitary-adrenocortical function, c ardiovascular tone, metabolic balance, fluid/electrolyte status, parturitio n and lactation. In all cases, a substantial component of this function is controlled by glutamate neurotransmission. In this study, the authors perfo rmed a high-resolution in situ hybridization analysis of ionotropic glutama te receptor subunit expression in the PVN and its immediate surround, N-met hyl-D-aspartate (NMDA) receptor 1 (NMDAR1), NMDAR2A, and NMDAR2B mRNAs were expressed highly throughout the PVN and its perinuclear region as well as in the subparaventricular zone. NMDAR2C/2D expression was limited to subset s of neurons in magnocellular and hypophysiotrophic regions. In contrast wi th NMDA subunit localization, AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxaz ole-propionate)-preferring and kainate (KA)-preferring receptor subunit mRN As were expressed heterogeneously in the PVN and surround. Glutamate recept or 1 (GluR1) mRNA labeling was most intense in preautonomic subregions, whe reas GluR2, GluR4, GluR5, and KA2 were expressed in hypophysiotrophic cell. groups. It is noteworthy that GluR5 mRNA expression was particularly robus t in the dorsolateral region of the medial parvocellular PVN, suggesting lo calization in corticotropin-releasing hormone neurons. All four AMPA subuni ts and GluR6 and GluR7 mRNAs were expressed highly in the perinuclear PVN r egion and the subparaventricular zone. These data suggest the capacity for multifaceted regulation of PVN function by glutamate, with magnocellular ne urons preferentially expressing NMDA subunits, preautonomic neurons prefere ntially expressing AMPA subunits, and hypophysiotrophic neurons preferentia lly expressing KA subunits. Localization of all species in the perinuclear PVN suggests that glutamate input to the immediate region of the PVN may mo dulate its function, perhaps by communication with local gamma-aminobutyric acid neurons. J. Comp. Neurol. 422:352-362, 2000. (C) 2000 Wiley-Liss, Inc .