Immunohistochemical observation on substance P in regenerating taste buds of the rat

The present study was performed to investigate the relationship between substance P-positive (SP-positive) nerve fibers and regeneration of taste buds in the foliate papillae of the rat by means of immunohistochemistry. It was confirmed by neurotomy that taste buds in the foliate papillae of the rat were innervated mostly (90%) by the glossopharyngeal (IXth) nerve and partly (10%) by the chorda tympani. In this experiment, the IXth nerve was sectioned distal to the petrosal ganglion. The rats were sacrificed at various intervals from 20 days to 80 days after the operation. In the course of degeneration and disappearance of taste buds, both SP-positive fibers and taste buds disappeared completely from the posterior folds of the foliate papillae 7 days after the operation. Within 22 days, regenerated SP-positive fibers began to appear in the lamina propria, and following the penetration of the fibers into the epithelium, taste bud anlagen reappeared at the bottom of the trench, and in the posterior folds at 24 days. The process of new taste bud formation extended toward the apex of the trench and to the anterior folds, which seemed to follow the regeneration in the nerve trunk. Quantitative data showed a gradual increase in the number of taste buds and taste buds containing SP-positive fibers. These findings indicate that SP might have a role in regeneration of taste buds.