味神経切断, 吻合後の茸状乳頭ならびに味蕾の変化に関する電子顕微鏡的研究

Abstract

The fungiform taste buds and some mechanosensory endings in rabbits, which are supplied with chorda tympani and lingual nerves, were examined by means of light and electron microscopy. Three to seven taste buds were present in the dorsal epithelium of a fungiform papilla. The taste bud was composed of the type I, the type II, the type III cells and the basal cells. The type III cell was characterized by the presence of dense-core vesicles and synaptic vesicles, and showed afferent synaptic contact with nerve endings. Thus, it was suggested that the type III cell is involved in the chemoreceptive function. The presence of numerous free nerve endings in the extragemmal epithelium and mechanosensory endings, and of encapsulated corpuscles and Ruffini-like endings in the connective tissue of the fungiform papillae suggested that the fungiform papillae of the rabbit were highly adapted to both taste and mechanical sensation. The fungiform papillae were examined by light and electron microscopy from 1 week to 6 months after denervation followed by microsurgical reinnervation of both chorda tympani and lingual nerves. Further, these results were compared with those of experiments which were carried out in the same manner except for the microsurgical reinnervation. The first remarkable finding was the appearance of an ulcer in the dorsal surface of the tongue of the denervated side after the first week following denervation. The ulcer remained visible for about 10 weeks after the operation, and a severe defect of the tongue of the denervated side was observed occasionally. Taste buds and mechanosensory endings in fungiform papillae disappeared completely after the first week following denervation. The dorsal epithelium of the fungiform papillae showed filiform-like structures because of the hyperparakeratotic changes. However, 15 weeks after denervation followed by microsurgical reinnervation, the fungiform papillae regained their normal appearance. Encapsulated corpuscles and Ruffini-like endings regenerated in the connective tissue of reinnervated fungiform papillae in this experimental period, although these nerve endings were small in size and in number. 5 months after microsurgical reinnervation, regeneration of the taste buds was observed in the dorsal epithelium of the fungiform papillae. Ultrastructure of regenerated taste buds was essentially identical with that of normal taste buds, although the numbers of regenerated taste buds and their constituents were smaller than those of normal fungiform taste buds. In groups where no microsurgical reinnervation was carried out, regeneration of mechanosensory endings in the connective tissue was observed 5 months after denervation. Regeneration of taste buds, however, could not be observed during the experimental periods, even 6 months after denervation. The present study showed morphologically that the rapid and reliable regeneration of taste buds and mechanosensory endings in denervated fungiform papillae by chorda tympani-lingual nerves could be expected only when the proximal and distal cut ends of these nerves were repaired microsurgically.