A monoamine in the gustatory cell of the frog's taste organ: a fluorescence histochemical and electron microscopic study.

Fluorescence histochemistry reveals that in the frog's taste organ a yellow fluorescence is regularly observed at the most basal region of the sensory epithelium. The fluorescence has a strong intensity, but it fades rapidly upon the UV-irradiation. The peak of the emission spectrum is at 520 mmug. Following reserpine treatment the yellow fluroescence is markedly reduced, but not depleted completely. From these characteristics the monoamine fluorescence is regarded as representing 5-HT (serotonin). The ultrastructural study on sensory epithelia shows that the terminal portions of gustatory cell processes are localized at the basal region. These portions are filled with dense cored vesicles (700-1000 angstrom in diameter) and frequently opposed with nerve fibers penetrating into the epithelium. The gustatory cell processes are also interposed between the terminal portions of nerve fibers. The cytoplasm of the gustatory cell process is characterized by many mitochondria, fine filaments and glycogen particles, but contains few cored vesicles. The distribution of terminal portions of gustary cell processes seems to correspond fairly well to that of the monoamine fluorescence observed discontinuously along the basal lamina. Accordingly it is concluded that the fluorigenic monoamine is localized in the cored vesicles of the gustatory cell.