In normal rats there is one taste bud on the apical surface of each fungiform papilla. These taste buds are innervated by the chorda tympani proper nerve (CT). According to general consensus, after cutting the nerve the taste buds should disappear. In this study, performed on 24 rats divided in six groups, the CT nerve on the left side (singly denervated) and the combined chorda-lingual (CT-L) nerve on the other side (doubly denervated were permanently interrupted. The animals were sacrificed after 5, 10, 20, 35,60 and 100 days and their tongues serially sectioned for light microscope examiation. Some papillae were examined under an electron microscope. The papillae were categorized into three groups: papillae with a normal looking taste bud, with an abnormal looking taste bud and without a taste bud. The results showed a substantial number of papillae with a normal looking taste bud present at all time intervals in all animals. More specifically, on the singly denervated side the proportion of normal looking taste buds stayed below 10% until day 60, when it increased to 15% and to 23% on day 100. The proportion of abnormal looking taste buds decreased from above 92% by day 5 to 49% on day 100. The percentage of fungiform papillae without signs of a taste bud was relatively low on the singly denervated side at times (1, 5, 16, 29, 34 and 28%). On the doubly denervated side fewer than than 4% normal looking taste buds were found throughout the time period. The proportion of abnormal looking taste buds decreased from ̃ 96% by day 5 to 35% on day 100. A significantly higher proportion of papillae with no taste bud was observed on this side from day 10 onwards. (1, 29, 32, 52, 60 and 63%). The reasons for the difference in tast bud number between the doubly and singly denervated sides are unknown, but it is possible that collaterals from other (non-gustatory) nerves have an ability, although limited, to induce and maintain fungiform taste buds. In other words, the capacity to induce taste bud formation is not limited exclusively to gustatory nerves.
Bibliographical noteFunding Information:
This study was supported by NIH Grant NS17021 and College of Agriculture and Life Sciences, University of Wisconsin, project 2962.