N-methyl-D-aspartate receptors on neurons that synthesize nitric oxide in rat nucleus tractus solitarii

The aim of this study was to determine whether neuronal nitric oxide syntha se and N-methyl-D-aspartate receptors are co-localized in the rat nucleus t ractus solitarii. Such co-localization would support the hypothesis that ni tric oxide participates in nucleus tractus solitarii-mediated functions, su ch as cardiovascular regulation, by a link to N-methyl-D-aspartate receptor s. We used double fluorescent immunohistochemistry using antibodies against neuronal nitric oxide synthase and N-methyl-D-aspartate receptor subunit I , the fundamental subunit for functional N-methyl-D-aspartate receptors. La beled brainstem sections were examined with confocal laser scanning microsc opy. Most of the N-methyl-D-aspartate receptor subunit 1 immunoreactivity w as in cell bodies and proximal dendrites of the numerous labeled cells in t he brainstem. High levels of N-methyl-D-aspartate receptor subunit 1 immuno reactivity were present in the dorsal motor nucleus of vagus, hypoglossal n ucleus and nucleus ambiguus. All subnuclei of the nucleus tractus solitarii contained moderate levels of N-methyl-D-aspartate receptor subunit 1 immun oreactivity. The distribution of neuronal nitric oxide synthase immunoreact ivity in the nucleus tractus solitarii was similar to that described in ear lier reports. Superimposition of images revealed that almost all neuronal n itric oxide synthase immunoreactive neurons in the nucleus tractus solitari i contained N-methyl-D-aspartate receptor subunit I immunoreactivity, but a lesser portion of N-methyl-D-aspartate receptor subunit 1-immunoreactive c ells contained neuronal nitric oxide synthase immunoreactivity. Although al l nucleus tractus solitarii subnuclei contained double-labeled neurons, the central subnucleus exhibited the highest density of double-labeled neurons . Co-localization of neuronal nitric oxide synthase and N-methyl-D-aspartare receptor subunit 1 in the nucleus tractus solitarii provides anatomical sup port for the hypothesis that N-methyl-D-aspartate receptor activation can a ffect nucleus tractus solitarii controlled functions via actions on neurons that synthesize nitric oxide. (C) 2000 IBRO. Published by Elsevier Science Ltd. All rights reserved.