PROJECT SUMMARY / ABSTRACT The long-term goal of this project is to reveal basic neurobiological mechanisms about how vagal sensory neurons find, innervate, and interact with specific end-organs and tissues during development. Sensory neurons of the vagus nerve detect and transmit diverse signals from internal organs, including ingested nutrients, changes in blood pressure, and mechanical distension of the stomach. Anatomically, it is a uniquely long cranial nerve that emanates from a single pair of ganglia near the hindbrain yet courses through the entire body and innervates a myriad of target tissues. From these ganglia, each vagal sensory neuron sprouts a single pseudounipolar axon that targets a specific internal organ peripherally and a dedicated brainstem circuit centrally. Faithfully establishing this connectivity is essential for neural control of physiological functions such as breathing, heart rate and digestion. Despite its vital role and the emerging importance of brain-viscera communication, it remains largely unknown how the intricate anatomical structure of the vagus nerve forms during development, and whether miswiring of the vagus nerve may contribute to diseases of the autonomic nervous system. This project proposes to leverage novel genetic and advanced imaging techniques to begin addressing the long-term goal by combining anatomical (Aim 1), cellular (Aim 2), and molecular (Aim 3) approaches. Aim 1 will establish a comprehensive, high-resolution map of vagus nerve development in the context of the whole animal, by utilizing genetic labeling, tissue clearing, and high- resolution microscopy. Aim 2 will elucidate the interplay between enteric neuron migration and vagal afferent outgrowth, by utilizing cutting- edge mouse genetics tools to selectively manipulate different cell types. Aim 3 will identify molecular determinants of vagus nerve pathfinding, by combining publicly available data and mouse genetics tools to label and perturb candidate gene expression in vagal sensory neurons. It is becoming increasingly apparent that vagus nerve connectivity plays a role in metabolism and energy homeostasis, with implications in related disorders. Therefore, results of this project will open new lines of inquiry on how viscera-to-brain communication is established and maintained in health and disease.!