Taste receptor end-organs have long been recognized to depend upon their innervation for maintenance of their structural integrity. Indeed, taste bud degeneration following denervation is, perhaps, the most commonly cited example of neurotrophism for the sensory nervous system. Recent anatomical studies, however, have raised questions about the nature of the structural changes that occur in taste buds after interruption of the gustatory nerves. Notably, in the hamster, fungiform taste buds persist after chorda/lingual denervation although the denervated buds exhibit measurable morphological changes including atrophy and disruption of the taste pore. Apparently, the degree to which the structural integrity of taste buds depends on innervation differs dramatically between species and papillae. Factors accounting for this difference will be investigated in this project. The magnitude of taste bud degeneration following denervation might be related to the rate of cell turnover in the bud. This will be evaluated with tritiated thymidine autoradiography. Intermediate high voltage electron microscopy will establish the ultrastructural types of cells generated in denervated taste buds. The possibility that denervation may be incomplete or impermanent following gustatory nerve resection in hamsters will be evaluated with routine electron microscopy and labelling studies. The proposed labelling studies will employ injections of cholera toxin or fluorescent tracers to determine the ganglionic sources of nerve fibers that innervate taste buds before, or may innervate buds long after, chorda/lingual denervation. These studies will provide basic information concerning nerve-taste bud interactions. The studies are relevant to an understanding of how nerves maintain taste buds, and they have implications for explaining the relative vulnerability of permanence of taste compared with other sensory systems.
