The effect of glossopharyngeal nerve transection on the taste buds of the rat vallate papilla

The effect of glossopharyngeal nerve transection on the taste buds of the rat vallate papilla was examined by using the method of DNA nick-end labeling (TUNEL) and standard electron microscopic technique at 1, 3, 5, 7, 9 days after denervation. In general, the number and size of taste buds decreased as more days passed after denervation. They started decreasing on day 3 post denervation and virtually all taste buds were disappeared on day 9 post denervation. In studies using TUNEL method, TUNEL postive cells markedly increased in their numbers one day post denervation, as compared with controls. The number of apoptotic taste bud cells per taste bud profile was averaged to be 0.64 and 0.44 for day 1 and 3 post denervation, respectively, whereas it was 0.10 in controls. In electron microscopy, apoptotic cells were identified by the presence of condensed and fragmentary nuclei in a cytoplasm, which resulted in increased density. In control rats, only few apoptotic cells were found. On days 1 and 3 post denervation, nerve fibers almost disappeared from the taste buds and some apoptotic cells were apparent. On days 7 and 9 post denervation, a few taste bud cells were still present in the epithelium of the bottom of the trench wall of the vallate papilla and most of them showed apoptotic changes. The results indicate that the death of taste bud cells in normal conditions is controlled by apoptosis and the decrease and disappearance of taste buds after denervation is also caused by apoptosis of taste bud cells.