| Taste buds in the gustatory system are dependent on innervation for maintenance of structure and function, but the mechanism of nerve-target interaction remains unclear. Studies of fungiform taste bud development utilizing "knockout" mice have began to successfully elucidate molecular mechanisms of early innervation. Far fewer studies have been done with adult mice, and have been limited to circumvallate taste buds. For example, the pro-apoptotic gene bax has been implicated in taste bud cell death and bax null mutant (bax-/-) mice have a dramatic increase in circumvallate taste bud size compared to wild-type mice. However, the study of fungiform taste buds offers experimental advantages over circumvallate taste buds. For example, the discrete grouping of taste buds in fungiform papillae makes permits non-invasive experimental manipulations with single taste buds. The current set of studies characterized size and distribution of fungiform taste buds in adult C57BL/6J and bax -/- mice in both intact taste systems and 5--20 days after unilateral chorda-lingual nerve transection. After nerve transection, taste buds on the ipsilateral tongue decreased in size and number, while contralateral taste buds increased in size. While more posterior regions of the tongue had nearly a complete loss of taste buds by 15 days post-transection, 50% of the taste buds on the anterior-most millimeter of tongue still remained 20 days post-transection. Remaining taste buds could not be explained by innervation; nerve fibers in fungiform papilla were not present 10 days after transection. The presence of the non-functional bax gene resulted in larger taste buds, but did not rescue taste buds from the effects of denervation. In addition, bax-/- mice had the same number of chorda tympani neurons innervating the anterior tongue as wild-type mice, with similar mean number of neurons innervating individual taste buds. Thus, bax was not necessary for injury-induced fungiform taste bud cell death. These data are essential for future studies that identify nerve-target interactions in the mouse. |
