The dependence of taste buds on innervation has been used as a model to understand nerve/target 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. 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. Collectively, these findings show that the adult peripheral and central gustatory system is especially plastic at adulthood. Coordinated studies will focus on the injury-induced plasticity in gustatory neurons at their peripheral and central targets. To begin addressing candidate mechanisms that may underlie these events, a key focus of proposed studies is to examine the role of Brain Derived Neurotrophic Factor (BDNF) on maintaining the morphological and functional characteristics of gustatory neurons at adulthood, and on degenerative/regenerative processes that are attendant to sectioning the chorda tympani nerve (CTX). Combined anatomical, neurophysiological, molecular genetic, and cellular/molecular techniques in experiments using rats and mice sustaining unilateral CTX will permit us to: 1) determine the CTX-induced functional plasticity in the NST by recording central taste responses while stimulating individual, distinct taste receptor populations;2) determine how maintenance of the peripheral and central gustatory system is altered when BDNF is removed from lingual epithelia at adulthood, and how this removal affects CTX-induced degeneration and regeneration of the system, and 3) determine how maintenance and CTX-induced degeneration and regeneration of the peripheral and central gustatory system is affected when BDNF is removed from most tissues at adulthood, including lingual epithelia, the geniculate ganglion, and the NST. 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.
