Ultrastructural and histochemical studies on the taste buds in some reptiles

The taste buds in tortoises (Clemmys japonica and Geoclemys reevesii), lizards (Takydromus tachydromoides) and snakes (Elaphe quadrivirgata) were examined by both ultrastructural and histochemical methods. The taste buds consisted of at least three types of cells: the type I, II and III cells. The type I cells were characterized by the presence of secretory dense granules containing polysaccharides which were demonstrated by periodic acid-chromic acid-silver methenamine technique. The type II cells contained numerous tubular, vesicular and lamellated structures. The type III cells were characterized by dense cored vesicles and afferent synaptic contacts. Besides these cells, basally located cells which resembled the basal cells of other lower vertebrates were sometimes found in the tortoises. After administration of L-DOPA following nialamide, some taste bud cells of the tortoises, Clemmys japonica, showed weak yellowish green fluorescence by monoamine fluorescence histochemistry and the dense-cored vesicles in the type III cells increased in number. Acetylcholine esterase activity was not observed in tortoise taste buds. It is suggested that the three types of cells which compose the taste buds of the reptiles may correspond to the three types of cells in mammalian, and the type III cells represent the gustatory cells which are able to potentially produce biogenic monoamines. From these results, the taste buds of the reptiles may hold an intermediate position between those of mammals and amphibia or fishes.