DESCRIPTION: (Adapted from the application) The control of the vascular system by the sympathetic nervous system depends on the organization of sympathetic neurons into function-specific pathways. The postganglionic sympathetic neuron plays a critical role in this organization. Characteristic morphological, neurochemical and electrophysiological features of these sympathetic neurons contribute to their specific functional pathways. Although it is known that sympathetic neurons in vascular pathways have distinct neurochemical characteristics, it is not known whether there are distinctions between neurons innervating arteries and veins. The functional separation between vascular resistance and capacitance is an important part of cardiovascular regulation. Four specific aims are proposed: 1. Test the uniqueness of the localization and transmitter phenotype of the neurons in prevertebral ganglia that innervate mesenteric arteries and veins. 2. Test the uniqueness of the electrophysiological characteristics of the neurons in prevertebral ganglia that innervate mesenteric arteries and veins. 3. Characterize the source and effects of selected sensory neurotransmitters in prevertebral ganglia that are related to the target organ (artery or vein). 4. Compare the release of ATP from sympathetic nerves innervating mesenteric arteries and veins. Achieving the objectives will define the nervous mechanisms underlying the separate control of resistance and capacitance vessels. The splanchnic circulation receives 30% of the cardiac output and contains about one-third of the total blood volume. In essential hypertension, vascular capacitance is initially reduced and this is followed by changes in resistance. The studies outlined in this proposal will enhance our understanding of the underlying mechanisms of this and related phenomena.