The mammalian taste bud type III cell: a critical analysis.

Rabbit foliate tissue fixed in 2% paraformaldehyde and 2% glutaraldehyde, postfixed in OsO4, was embedded in Epon and sectioned and stained with uranyl acetate and lead citrate for ultrastructural analysis. Favorable serial sections contained an entire type III cell, demonstrating for the first time in a single preparation its most characteristic features. These are cytoplasm containing specific dense-cored vesicles concentrated in the base, masses of synaptic vesicles near typical chemical synapses with nerves, and the upper part of the cell ending in a blunt extension beyond the dense substance. It is emphasized in particular that specific dense-cored vesicles denote type III cells and larger dark granules denote type I cells. It is postulated that the type III cell is a special, but is not necessarily the only, gustatory receptor cell. Previous evidence from this and other laboratories is systematically reviewed to substantiate the validity of the cell type.