MICROVILLAR CELLS OF THE OLFACTORY EPITHELIUM - MORPHOLOGY AND REGENERATION FOLLOWING EXPOSURE TO TOXIC COMPOUNDS

In recent years microvillar cells (MVC) have been identified in the ol factory epithelium of numerous species, including rodents, canines, an d primates. However, there is no consensus on the morphologic or histo chemical features of this cell, nor is the function of these cells cur rently known. Previous studies have examined MVC during development an d in the mature olfactory epithelium, but not after toxic insult. A mi crovillar cell, defined by specific morphologic criteria, was studied in adult male Long-Evans rats exposed via inhalation to either 200 ppm methyl bromide for 4 h/day, 4 days/week for 2 weeks, or to 635 mu g/m (3) nickel for 6 h/day for 16 consecutive days, and sacrificed seriall y over several months. The pattern of recovery for MVC differed accord ing to the severity and specificity of the insult to the olfactory epi thelium. With methyl bromide, all cell types were completely depleted from olfactory epithelium immediately after injury, including MVC. MVC were slow to repopulate the epithelium, and appeared only when olfact ory epithelium was complete in other respects. With nickel exposure, w here the major effect was a gradual decrease in sustentacular cells wi th a thinning of the apical cytoplasm thickness, MVC showed a decline during exposure, but reappeared during recovery. In both cases, there was no difference in olfactory function, even when MVC were absent fro m the olfactory epithelium. A mature olfactory epithelium appears to b e necessary to support the presence of this MVC, suggesting that it is not crucial to the regeneration processes or recovery of olfactory fu nction, but perhaps plays some role, as yet undefined, in the unpertur bed olfactory epithelium.