Olfactory receptor cells: immunocytochemistry for nervous system-specific proteins and re-evaluation of their precursor cells.

The immunohistochemical localization of nervous system-specific proteins and cytokeratin in the olfactory mucosa is described mainly in humans and guinea pigs. Immunoreactivity for neuron-specific enolase (NSE) was demonstrated in olfactory receptor cells including their dendrite and axon. Immunoreactivity for neurofilament protein (NFP) was contained in the dendrite and perikaryon of the olfactory cells, but not in the axon. Immunoreactivity for spot-35 protein, a kind of neuron-specific proteins was selectively localized in several flask-shaped cells of the olfactory epithelium only in the guinea pig. These spot-35 protein-positive cells were suspected of being microvillar cells, considered the second type of receptor cells dispersed in the olfactory epithelium. Immunoreactivity for glia-specific S-100 protein was demonstrated in the Bowman's glands as well as Schwann cells associated with the olfactory nerves in the lamina propria. Supporting cells were not immunolabelled with any antisera against nervous system-specific proteins. Cytokeratin, a useful marker for epithelial cells, was expressed exclusively in basal cells. Axotomy of olfactory nerves induced the disappearance of the olfactory receptor cells with NSE immunoreactivity 3 days after the operation. Regenerating cells showing NSE immunoreactivity were first recognized in the lower portion of the epithelium within 7 days. The epithelium was completely repaired 3-4 weeks later and came to contain many NSE-reactive mature receptor cells. Bromodeoxyuridine (BrdU), administered during regeneration of the olfactory epithelium, was immunohistochemically detected in the cells of the layer above the basal cell layer, but not in the latter itself. This result does not support the general contention that the receptor cells originate from the basal cells.