Olfactory and nasal respiratory epithelia, and foliate taste buds visualized with rapid-freeze freeze-substitution and Lowicryl K11M embedding. Ultrastructural and initial cytochemical studies.

Rat olfactory and respiratory epithelia and Rhesus monkey taste buds were studied with rapid-freeze, acetone/0.1% uranyl acetate freeze-substitution and low-temperature Lowicryl K11M embedding, usually in the absence of other chemical fixation and cryoprotection procedures. Ultrastructural features of mucus, cytoplasm, including cytoskeletons, and membranes were better retained than with conventional methods. Some major examples: The mucus of the olfactory epithelium consisted of a single layer; that of the respiratory epithelium had an electron-opaque sol layer surrounding cilia and microvilli below a thin laminated electron-lucent gel layer. Taste-bud pores displayed a foam-like opaque secretory product, resembling the contents of secretory granules within Type I taste-bud cells. The electron-opacity of cytoplasmic matrices sometimes obscured features such as radial spokes of respiratory cilia. Membranes had smooth outlines; those of olfactory receptor cell cilia were more electron-opaque than those of olfactory supporting cell microvilli and respiratory cilia. Membranous monolayers of many respiratory cilia across large arrays often partially split apart, all in the same direction. The space between those monolayers contained an electron-lucent substance. Preliminary cytochemistry on olfactory and nasal respiratory epithelial samples with the lectin Concanavalin A (Con A) and antibodies against olfactory marker- and odorant-binding proteins and, in taste only, the sweet-tasting protein thaumatin, were sufficiently successful to warrant further endeavors.