Afferent projections of trigeminal, facial, and glossopharyngeal nerves, which innervate lingual taste papillae, enter the hindbrain via the solitary tract and terminate in the solitary nucleus in a topography that reflects peripheral organization. How and when these sensory afferents are initially organized in the solitary tract are not well understood. Given the importance of an organized taste system for proper function, the long-term objective is to determine how the solitary tract is established. The scope of the proposed research aims to determine the developmental time course and distribution of sensory afferents comprising the solitary tract and to localize glia in relation to this development. To accomplish this, combinations of sensory ganglia will be labeled and solitary tract projections will be visualized in three dimension at a series of embryonic stages. Astrocytic glia will be immunohistochemically identified across developmental stages and correlated with solitary tract development for a role as a potential guidance factor. The working hypothesis is that taste and tongue nerve projections initially are separate from each other and gradually acquire extensive overlap within the solitary tract. Tract tracing via carbocyanine dyes and immunohistochemistry will be used to examine the organization of the solitary tract and to identify the relative location of astrocytes. The results of these experiments will provide a simultaneous, physical representation of the association of sensory afferents within the solitary tract and will demonstrate a possible cellular, astrocytic contribution to the organization of these afferents within the solitary tract. Potentially, the initial organization of sensory afferent projections in the solitary tract dictates the eventual organization of the associated terminal fields in the solitary nucleus. Therefore, these results will provide an important foundation for understanding the establishment of the primary afferent relay of the gustatory system. Taste sensation, which guides nutritive choices and ingestive behaviors of all vertebrates, is transduced by peripheral receptors and conveyed directly through the solitary tract to the medulla where it is integrated with other sensory inputs. Thus, a thorough knowledge of the organization of afferent projections within the solitary tract will contribute to a more complete understanding of how taste information is integrated in the central nervous system to inform diet choices, a behavior essential to sustain life. [unreadable] [unreadable] [unreadable]