Possible role of serotonin in Merkel‐like basal cells of the taste buds of the frog, Rana nigromaculata

Merkel‐like basal cells in the taste buds of the frog were examined by fluorescence histochemistry, immunohistochemistry and electron microscopy. There were about 16–20 basal cells arranged in a radial fashion at the base of each taste bud. These cells were strongly immunopositive for serotonin antiserum. They were characterised by the presence of numerous dense‐cored granules in the cytoplasm ranging from 80 to 120 nm in diameter, and of microvilli protruding from the cell surface. For 4 mo after sensory denervation by cutting the gustatory nerves, all cell types of the taste bud were well preserved and maintained their fine structure. Even at 4 mo after denervation, the basal cells exhibited a strong immunoreaction with serotonin antiserum. To investigate the function of serotonin in the basal cells in taste bud function, serotonin deficiency was induced by administration of p ‐chlorophenylalanine (PCPA), an inhibitor of tryptophan hydroxylase, and of p ‐chloroamphetamine (PCA), a depletor of serotonin. After administration of these agents to normal and denervated frogs for 2 wk, a marked decrease, or complete absence, of immunoreactivity for serotonin was observed in the basal cells. Ultrastructurally, degenerative changes were observed in both types of frog; numerous lysosome‐like myelin bodies were found in all cell types of the taste buds. The number of dense‐cored granules in the basal cells also was greatly decreased by treatment with these drugs. Serotonin in Merkel‐like basal cells appears to have a trophic role in maintenance of the morphological integrity of frog taste bud cells.