Degeneration and Regeneration of the Olfactory Epithelium in the Mouse-A Scanning Electron Microscopic Study-

Morphological changes of the olfactory epithelium in the mouse due to aging, formaldehyde gas and sectioning of the fila olfactoria were studied by scanning electron microscopy. In the normal olfactory epithelium many cells with stereocilia like microvilli were observed.These cells resembled the fifth cell of the cat found by Andres (1969) and appeared to be mechano-receptors in the olfactory epithelium. Morphological changes due to aging were characterized by increase of the respiratory ciliated cells in the olfactory region and retreat of the olfactory epithelium at its boundary with the respiratory epithelium. The olfactory epithelium was variously affected after exposure to formaldehyde gas. In areas with severe damage the supporting cells degenerated early. This area regenerated to respiratory ciliated epithelium 14 days after exposure.Areas in which the supporting cells were not affected finally regenerated to olfactory epithelium.Transformation to ciliated cells in the olfactory region after formaldehyde gas exposure suggests that the basal cells of the respiratory and olfactory epithelium and the duct cells of Bowman's gland might be the stem cells of regenerated ciliated cells. Neuronal degeneration after sectioning of the fila olfactoria was recognized one day after surgery, and regeneration was noted 14 days after axonotomy.Regeneration to the normal surface structure of the olfactory epithelium was observed 56 days after axonotomy, but regeneration of the whole surface was still imcomplete at this stage.Morphological changes in the surface of the supporting cells were also recognized after surgery, but these findings were probably caused by reactive changes due to disappearance of the mat of the olfactory cilia. In several specimens a wide olfactory region was covered with respiratory ciliated epithlium after axonotomy,but it is questionable that these transformations were produced only by sectioning of the fila olfactoria .

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