LIGHT AND ELECTRON-MICROSCOPIC DEMONSTRATION OF METHYLENE-BLUE ACCUMULATION SITES IN TASTE-BUDS OF FISH AND MOUSE AFTER SUPRAVITAL DYE INJECTION

Electron microscopical data regarding methylene blue staining of taste buds in the epithelia of the goldfish lip and the cirumvallate papill a of the mouse tongue after supravital dye application are presented f or the first time. The ultrastructural details were compared with the corresponding light microscopical findings. The dye was applied in dif ferent concentrations by injection or in crystalline form directly to the surface of the tissues. Both methylene blue and tissue were simult aneously fixed by immersion in a paraformaldehyde-glutaraldehyde solut ion with the addition of phosphomolybdic acid. The ensuing dye precipi tate was further stabilized by ammonium heptamolybdate. On the light m icroscopical level, the taste bud's receptive structures, i.e. the rec eptor area (fish) and the taste pit (mouse), exhibited the highest aff inity for the dye. Additionally, the mucous material within the trench es around the circumvallate papillae in mice was intensely stained. On the electron microscopical level, the cationic phenothiazine dye boun d to the receptor villi or to the mucus coating the receptive structur es. In the case of higher dye concentrations, a staining of single tas te bud cells took place starting apically and proceeding down to the b ase. Dye accumulations within the intercellular clefts between the epi thelial cells or within other structures were observed only if the dye concentration was further increased. Since similar results were also obtained with the cationic phenazo dye Janus green, dye accumulation i n the mucus covering the receptor villi may be representative of the g eneral binding of organic cations, which are known to induce bitter ta sts sensations.