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The present work was designed to study the histological changes of the rat’s circumvallate papilla following unilateral glossopharyngeal re-innervation. Unilateral re-innervation was achieved by transection of the 9th nerve and avulsion of its central segment on the right side and crushing that of the left side. The latter was thus allowed to regenerate and to re-innervate the papilla. On the first 2 post-operative weeks, the nerve bundles at the base of the papilla and the subgemmal nerve plexus showed signs of Wallerian degeneration and concomitant disappearance of taste buds. On the 3rd post-operative week, the papilla was invaded by regenerating nerves and the primordial taste buds started to appear. From the 4th week onwards, the number of regenerating taste buds on the left outer, left inner and right inner trench walls was not significantly different from the sham-operated controls. The only buds which failed to reappear were those of the upper two thirds of the right outer trench walls. The newly formed buds were smaller in size than those of the sham-operated controls with a relative diminution of 30% of the number of intragemmal cells per section of taste bud.

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The present work was carried out to study the effect of the length of the distal stump of transected nerve upon the rate of degeneration and the time course of disappearance of mammalian taste buds. Twelve adult rabbits were anaesthetized and the glossopharyngeal nerves of both sides were exposed and transected so as to leave a long distal stump on the right and a short one on the left side. The animals were sacrificed at different post-operative periods ranging from 2 to 14 days and the circumvallate and foliate papillae of both sides were examined. The taste buds on the side of the short distal stump always showed a greater decrease in number, size and cell contents than those of the side of the long distal stump. The taste buds on the side of the short distal stump disappeared earlier than those of the side of the long distal stump. Vallate taste buds disappeared earlier than the foliate: possible reasons for this were put forwards. The validity of the neurohumoral theory to the mammalian taste buds was discussed.

Twenty-five rabbits were used to study the effect of glossopharyngeal nerve transection upon the number, size and cellular constitution of the taste buds. The glossopharyngeal nerve was cut o n one side, the other being left undisturbed as a control. The animals were sacrificed i n groups of three after 7, 10, 14, 21, and 30 days, and 2 and 4 months after the operation. Seven days after the operation the size and number of intragemmal cells were decreased in the taste buds. The taste pores with hairlets passing through them disappeared. The number of taste buds on circumvallate papillae decreased. After ten days taste buds in both types of papillae showed signs of degeneration. Fourteen days after the operation there was a marked decrease in size and number of taste buds. The circumvallate papillae now possessed no taste buds. After 21 days few taste buds were present in foliate gutters. These consisted of one or two sustentacular cells each. After 30 days there were no taste buds on foliate papillae, and thickness of the epithelium lining the gutters was decreased. Two or four months after denervation, the foliate gutters were shallow and some had become flattened. The importance of the gustatory nerve for development and maintenance of the normal status of the taste buds is discussed.Many investigators (Meyer, 1897; Olmsted, '20, '21, '22; Whiteside, '26; Torrey, '34, '40; Guth, '57, '58) have confirmed the observation that mammalian taste buds disappear after denervation and reappear following regeneration of the supplying gustatory nerve. Robbin ('67) stated that after denervation of frog taste buds, there was shrinkage and decrease in their size. He also postulated that the gustatory nerve was concerned with maintenance of adult cells, and control of DNA synthesis and mitosis of germinative cells. Several investigations have been performed to determine whether non-gustatory nerves can also stimulate the development of taste buds. The lingual nerve was used in the hedgehog (Boeke, '17) and dog (Olmsted and Pinger, '36; Arey and Monzingo, '42). In each of these studies, hypoglossallingual nerve anastmosis was performed, directing the regenerating hypoglossal fibers to the lingual epithelium. The results of these studies were varied. Guth ('58) using the glossopharyngeal nerve in the cat, concluded that all but a small number of taste buds on the ipsilateral circumvallate papillae disappeared after unilateral transection of the nerve. Re-appearance of taste buds occurred upon re-innervation of the papillae by either the glossopharyngeal or vagus nerve, but re-innervation by the hypoglossal nerve did not induce formation of taste buds. In spite of the extensive studies concerning the taste bud-nerve fiber relationship, insufficient information has been reported about the changes in cellular constitution of taste buds after denervation. The present work was undertaken to study the sequential cellular changes in taste buds after denervation, and, to confirm the trophic effect of the gustatory nerve upon ...