(Verbatim from the application): Glutamate is the major neurotransmitter in primary afferents to the nucleus of the solitary tract (NTS), including baroreceptive afferents. The proposed studies will examine the receptor substrates for glutamatergic excitation of neurons involved in central autonomic control at sensory sites in the NTS. Since the ionotropic receptors have been most strongly implicated in regulating autonomic responses in the NTS, we will first characterize the cellular distribution of each of these receptors in the medial NTS, the primary termination site for baroreceptor afferents (Aim 1). The anatomical location of each receptor is fundamentally related to its functional role (e.g. presynaptic receptors regulate release from axon terminals, while postsynaptic receptors mediate excitatory responses). The proposed studies will use immunocytochemical localization of receptor proteins from three types of ionotropic glutamate receptors (NMDA, AMPA and kainate). Electron microscopy will resolve the subcellular location of these receptive sites. Baroreceptor afferents contained in the aortic depressor nerve (ADN) are involved in cardiovascular autonomic regulation, so anterograde labeling of these afferents will be used to identify autonomic neurons in the NTS (Aim 1.b). The glutamate receptor distribution on these afferents and their targets will be examined. In other studies, second-order baroreceptive NTS neurons, which show monosynaptic responses to stimulation of the solitary tract in the slice preparation and are apposed by anterogradely labeled boutons from the ADN, will be intracellularly filled and the glutamate receptor will be immunocytochemically localized on the same cell (Aim 1 .c). To assess their role in central autonomic plasticity, glutamate receptor subunits that are located in NTS autonomic neurons will be quantitatively examined after chronic hypertension for signs of receptor up- or down-regulation, or internalization, using both optical densitometry and immunocytochemical receptor labeling with electron microscopy (Aim 2). The goal of this project is to understand the cellular substrates for regulation of NTS autonomic neurons both spatially (over the surface of the cell) and temporally (in different physiological states), and to relate this structural information to the physiological properties of these neurons. These studies will establish a structural basis for acute and chronic plasticity in NTS. The long-term goal of this project is to understand the cellular basis for receptor modulation of central autonomic neuronal activity.
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