WIKLUND, J.M.; Idaho State University: INNERVATION OF THE LOWER JAW IN Xenopus laevis

The purpose of this study is to examine the neurons that innervate the hypoglossal nerve in the lower jaw of the frog, Xenopus laevis. Previous studies have shown that the hypoglossal nerve innervates the tongue protractor and retractor muscles in frogs. However, the clawed frog, Xenopus laevis, does not have a tongue. Our research identified and labeled the peripheral hypoglossal nerve and the location in the brain of the cell bodies. The frogs were anesthetized and an incision made to expose the hypoglossal nerve. This nerve was cut and a crystal of the fluorescent dye, FDA, was applied to the cut nerve ends. After a dye transport time of approximately 7 hours, frogs were euthanized and the head was immersed in fixative. The brain was then removed, placed in gelatin and sectioned. Sections were mounted on slides and examined under an epifluorescent microscope. Four separate populations of neuronal cell bodies were identified and counted. The four nuclei populations that showed evidence of dye uptake were the caudal ventrolateral, ventrolateral, ventrolateral/dorsomedial and dorsomedial nuclei. Previous work in other frogs has shown that these nuclei innervate different muscle groups in the frog tongue. Total number of nuclei in each population was compared to the numbers in tongued frogs. The data shows that the tongueless frog Xenopus, has more hypoglossal nuclei and a greater distribution of those nuclei than found in previously studied frogs. The function of this nerve in Xenopus remains to be discovered.