Taste buds provide a model system for the study of development, trophic maintenance, and regeneration because the differentiation and maintenance of taste receptor cells depends upon their innervation by gustatory nerves. In a variety of neural systems, cell-surface and extracellular matrix molecules have been shown to be important for cell-cell and cell-substrate contacts, which guide development and regeneration. Several cell-surface molecules are present on cells in the vallate, foliate, and fungiform taste buds of the adult rat. It has been established that this expression in the vallate taste buds is dependent upon innervation by glossopharyngeal nerve fibers. The studies proposed here are designed to characterize the distribution and regulation of cell-surface molecules within the various subpopulations of taste buds in the rat. In addition, the correlation of this expression with the normal development of taste buds and with their regeneration following peripheral nerve injury will be determined. The first specific aims is to characterize the expression of cell-surface molecules in taste buds innervated by cranial nerves VII, IX, and X and their regulation during normal development. The immunocytochemical localization o antibodies to neuronal cell adhesion molecules (NCAMs), extracellular matrix molecules (laminin, fibronectin),. globo- and lactoseries carbohydrates, and several other growth-dependent molecules (GAP43, vimentin, Thy-1) will be determined for different taste-buds bearing regions of epithelium. Taste buds in the fungiform papillae, the vallate and foliate papillae, and in the epiglottal region, innervated by the VIIth, IXth, and Xth cranial nerves, respectively, will be examined in adult rats. Since the development of taste buds in each of these regions begins at different times and proceeds at different rates, the time course of the expression of these molecules during normal development will be determined in order to test the hypothesis that their expression is developmentally regulated. The second specific aim is to study the expression of these cell-surface molecules during the regeneration of taste buds following peripheral nerve injury. The time course of this expression will be correlated with the reinnervation and regeneration of taste buds in the vallate papilla. To test the question of whether the expression of these molecules is determined by the innervating nerve fibers or by the target epithelium, taste buds in the vallate papilla. To test the question of whether the expression of these molecules is determined by the innervating nerve fibers or by the target epithelium, taste buds in the vallate and fungiform papillae will be immunocyto-chemically characterized following cross- reinnervation by the IXth and VIIth nerves.
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