The dependence of taste buds on innervation has been used as a model to understand nerve/tar interactions. Loss of innervation results in a loss of the normal morphological appearance of taste buds, while restoration of innervation results in a recovery of taste bud morphology and function. The adult regenerating gustatory system is especially susceptible to environmental manipulations. Combining unilateral chorda tympani nerve section and low sodium diet in adult rats results in a variety of functional and anatomical alterations in both taste buds and in the regenerating nerve. Furthermore, functional and anatomical alterations also occur in the intact, contralateral side of the tongue. In addition to injury-induced effects related to the peripheral portion of the chorda tympani nerve, there are also extreme morphological changes that involve the central portion of the sectioned nerve. Coordinated studies will take advantage of the remarkable functional and anatomical plasticity induced by combined unilateral chorda tympani nerve section and dietary sodium restriction. A systems-level approach will focus on neural plasticity in the adult rat gustatory system. Combined anatomical, neurophysiological, electron microscopic, and immunocytochemical techniques will permit a determination of: 1) the stability of innervation of single taste buds over time in normal adults and determine the accuracy of chorda tympani neurons in reinnervating their original targets; 2) the extent and nature of terminal field plasticity in the NTS; 3) the extent and nature of synaptic plasticity in the NTS; and 4) the functional consequences of unilateral chorda tympani nerve section and/or dietary sodium restriction on taste responses in the NTS. Findings from these studies will address the broader topics of sensory coding, the role of neural activity in maintenance of sensory function, and the temporal stability and accuracy of peripheral innervation under normal circumstances and in response to nerve damage. Results will also enable a clearer understanding of the neurobiological sequelae of human taste nerve damage sustained pathologically, or during middle ear or oral surgery.
