An electron microscopic study of the olfactory mucosa in the bat and rabbit.

The olfactory epithelium and the olfactory gland were electron microscopically observed in the bat and rabbit. 1. In spite of abundant tubular components of sER, the supporting cells show no cytological signs of secretory activity. Numerous long irregular microvilli which are protruded from the supporting cells into the mucous film covering the olfactory epithelium contain no axial filaments. From the outer leaflet of the plasma membrane covering these cells and their microvilli, numerous polypoid processes are projected into the mucous film. These newly identified delicate processes with an apical vesicular swelling about 200 A in diameter may be involved in an extension of surface area or in a microapocrine release of unknown substance. 2. Olfactory cell perikaryon extends an apical dendrite forming an olfactory vesicle (better to be called "dendritic bulb") and a basal neurite or axon. Basal bodies of olfactory cilia are contained in the dendritic bulb and provided with 3 types of appendages: one or occasionally 2 striated conical basal feet directed toward the center of the dendritic bulb, an occasional 1.2 mu long striated rootlet and 9 spokes which extend between the distal end of each of 9 triplets of the basal body and the surface plasma membrane. 3. The present study has first disclosed the so-called "large dense-cored vesicles" about 750-1,000 A in diameter in the perikaryons and axons of olfactory cells. The dendrite and axon contain numerous neurotubules and mitochondria, but no neurofilaments. Cytological differences between dendrite and axon consist in that the former contains scattering free ribosomes but no large dense-cored vesicles, while the latter contains no free ribosomes but some large dense-cored vesicles. 4. Undifferentiated basal cells containing no tonofilaments, which are supposed to differentiate through mitosis into "intercalated cells," are proposed in this paper. Electron-lucent intercalated cells show cytological characteristics of undifferentiated cells, and may probably be precursors of both olfactory and supporting cells. 5. In the bat and rabbit olfactory gland, the presence of an intraepithelial excretory duct surrounded by proper epithelial cells lacking in secretory function seems doubtful. The olfactory gland seems to lack a basement membrane. Secretory cells are in various stages of the secretory cycle, but no distinct cell types have been distinguished. Secretory granules of low density with dense cores support, together with their histochemical properties, the mucous nature of the olfactory gland in both species, though the rich tubular elements of sER may suggest a possible peculiar nature of their secretions. Rabbit secretory cells contain "dense rodlets," which are probably derived from the tubular sER. They are discharged by apocrine process into the glandular lumen.