A proper analysis of the central nervous system mechanisms involved in the control of breathing and autonomic function relies heavily on a complete understanding of the anatomical and physiological organization of neuronal groups that receive input and provide output for this system. The air of this project is to study the nature and location of vagal afferent fibers in the brain stem. In addition, the spinal projections of viscera will also be studied. In the past, investigations of sensory and motor terminations of the vagus nerve have posed great technical difficulty since these studies were based on degeneration techniques. The recently developed technique of intracellular marking of neurons with horseradish peroxidase following physiological identification has provided us with an excellent tool for examining the local dendritic morphology of physiologically identified neurons as well as the patterns of collateral arborization. In this project we intend to use this technique to examine both vagal afferents and their terminals as well as brain stem neurons. These studies will extent the currently ongoing research in the laboratory of the Principal Investigator on this project. The collaboration of Dr. Richter on this project will be most valuable in the inracellular studies, since Dr. Richter is the foremost authority on intracellular identification of neurons from the Medulla Oblongata. In this project we will conbine Dr. Kalia's expertise of anatomical identification of vagal afferents and using horseradish peroxidase with the physiological expertise of Dr. Richter. In addition some connectivity studies are proposed using the HRP-WGA conjugate which in addition to providing better localization of the injection sites also provides much greater sensitivity. In essence this project addresses the question: How do vagal afferents exert their influence on central brain stem mechanisms and where do these afferents terminate?