Reformation of taste buds by crossed sensory nerves in the rat's tongue.

OAKLEY, B. Reformation of taste buds by crossed sensory nervps in the rat’s tongue. Acta physiol. scand. 1970. 79. 88-94. Rat taste buds degenerate and disappear when their nerve supply is cut. Regeneration of the taste nerve fibres causes certain epithelial cells to differentiate into slender receptor cells comprising the taste bud. In this study by cross-union the glossopharyngeal (IXth) nerve was made to innervate the front of the tongue, and in other rats the chorda tympani nerve was forced to grow to the back of the tongue. ‘These cross-regenerated sensory nerves were able to cause differentiation of epithelial cells into taste buds, whose number and distribution were histologically determined 15 weeks postoperatively. The cross-innervating IXth nerve reestablished taste buds in the existing fungiform papillae in conformity with the normal number and distribution of taste buds at the front of the tongue. The chorda tympani, forced to innervate the hack of the tongue, reestablish in the foliae papillae more than 1.5 times as many taste buds as it normally innervates. The number of taste buds normally innervated by the chorda tympani must, therefore, be restricted by the capacity of the anterior tongue tissue to respond to this nerve’s influence. This study indicates that the distribution and total number of taste buds in the rat tongue is limited by the inherent nature of the tongue region being innervated (tissue-specific) rather than by the type of nerve supplying the taste buds (nervespecific). Taste buds on the rat’s tongue are located in three different types of papillae. The fungiform papillae are punctate spots 0.3 mm in diameter, which are distributed over the dorsal surface of the anterior two thirds of the tongue. They are especially numerous near the tip of the tongue, Each of the approximately 90 fungiform papillae found on each side of the tongue, contains, with rare exceptions, only one taste bud. All of the fungiform taste buds are innervated by the chorda tympani nerve (Fish, Malone and Richter 1944, Whiteside 1927). On the posterior tongue there is a single midline circumvallate papilla with several hundred taste buds embedded in both the inner and outer walls of the nearly circular trench or furrow surrounding the papilla. About 90 % of these taste buds receive bilateral innervation from both IXth nerves (Guth 1963, Whiteside 1927). The third kind of papillae that have taste buds are the foliate papillae on each side of the posterior tongue. These