We have localized immunoreactivity for neuronal nitric oxide synthase, glutamate, NMDAR1 receptor subunits, and GLUR1 receptor subunits in the nucleus tractus solitarii (NTS) of rats and have identified strong associations between glutamate and nNOS and between each of the receptor types and nNOS in NTS. Our pharmacological studies suggest that responses to activation of glutamate receptors in NTS represent integrated action dependent on a link between ionotropic glutamate receptor and nitric oxide mechanisms in the NTS. The current protocols utilize immunohistochemical light, confocal and electron microscopic techniques and pharmacological methods to test the hypothesis that baroreflex transmission through ionotropic glutamate receptors in the nucleus tractus solitarii depends on neuronal nitric oxide synthase and soluble guanylate cyclase. There are two multifaceted specific aims. First we seek to define physiological and anatomical relationships between glutamatergic baroreceptor transmission and nNOS in NTS. Second, we seek to define physiological and anatomical relationships between glutamate receptors and cyclic GMP in NTS. We anticipate these studies will demonstrate that cardiovascular responses elicited by activation of NMDA and non-NMDA ionotropic glutamate receptors in NTS will depend to a significant degree on an intact nitroxidergic system in NTS, that responses will be attenuated or lost with interruption of the latter system, and that baroreflexes will be attenuated by interruption of nitric oxide synthesis or transduction of nitric oxide signals through soluble guanylate cyclase. We anticipate that our anatomical studies will show, at the electron micrsocopic level, that ionotropic glutamate receptors are frequently associated with nNOS and soluble guanylate cyclase immunoreactivity. Metabotropic receptors may be similarly associated, but at the electron microscopic level we expect to find that the latter receptors lie presynaptically with respect to nNOS neurons while the former predominantly occur postsynaptically, i.e. on nNOS immunoreactive dendrites or neurons in NTS.
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