Regional differences in cell density and cell genesis in the olfactory epithelium of the salamander, Ambystoma tigrinum.

The olfactory epithelium undergoes continuous regeneration. The present quantitative study uses tritiated thymidine autoradiography to investigate regional differences in the rate of olfactory epithelial cell genesis in the tiger salamander. There was a significant gradient in the incorporation of thymidine from the posterior to the anterior in the nasal cavity: the posterior epithelium underwent cell genesis much faster than the anterior. Additionally, the posterior epithelium was thinner and contained fewer cells than the anterior, although the proportions of receptor, supporting and basal cells remained about the same throughout the epithelium. After 5 or 20 days most of the labelled cells were found in the basal cell layer, although there were a few labelled supporting cells. This confirms observations in other species that there are two populations of dividing cells in the olfactory epithelium: the basal cells which give rise to receptor cells, and the supporting cells. The gradients in epithelial thickness, receptor cells, and the rate of cell genesis parallel a gradient in responsiveness to odorants observed in electrophysiological studies (Mackay-Sim et al. 1982; Mackay-Sim and Shaman 1984). The significance of these anatomical and physiological gradients is presently unclear.