ULTRASTRUCTURE OF THE TASTE DISK OF THE AFRICAN CLAWED FROG, XENOPUS-LAEVIS (VOL 19, PG 433, 1994)

The taste disk (TD) of the African clawed frog has been investigated b y scanning and transmission electron microscopy and compared with that of other Salientia. Unlike other tongue-bearing species, the TD's of Xenopus are found especially in the mucosa of the mouth floor and the palate. They are not situated on the top of fungiform papillae. TD's a re surrounded by specific electron-lucent cells containing some secret ory vesicles. The TD's epithelium consists of mucus cells, wing cells, sensory cells and basal cells. The mucus cells are arranged in two la yers-one is lining most of the surface area (as usual in other frogs), and the other layer is situated directly beneath the first and may re ach the basal membrane. Mucus cells possess an irregularly shaped nucl eus and two populations of secretory vesicles, granulated and electron -lucent ones. The slender sensory cells reach from the basal membrane up to the TD's surface, the receptor area. Sensory cells apically bear either one rod-like process or a tuft of small microvillar processes. Sheet-like processes of wing cells embrace both superficial mucus cel ls and sensory cells. On the TD's base some electron-lucent processes of(degenerating?) sensory cells with numerous dense-cored vesicles are located immediately above the nerve fiber plexus. They show, as well as the more electron-dense cell processes of other sensory cells, syna pses to the plexus' nerve fibres. Merkel cell-like basal cells with sh ort spine like processes contain clusters of dense-cored vesicles and intermediate filaments. Taken together, the TD of Xenopus differs from that of the Ranidae in that they have a different equipment with mucu s cells and no ciliated cells surrounding the TD. The structure of win g cells, sensory cells and basal cells is similar to that as observed in other frog and toad TD's. Insofar, Xenopus as a popular laboratory animal may also serve for chemoreception tests and replace the highly protected Rana species.