Response of olfactory Schwann cells to intranasal zinc sulfate irrigation

The response of olfactory Schwann cells was assessed at 2, 4, and 7 days following intranasal zinc sulfate irrigation in 1-month-old mice. Ultrastructural and immunohistochemical observations showed dramatic differences between experimental and control mice which had been washed with saline intranasally. Two days after zinc sulfate treatment, many olfactory nerve bundles contained patchy areas of axonal degeneration, while the cell bodies of the olfactory Schwann cells appeared to have increased in electron density and to have shifted peripherally. Some of the cell bodies protruded from the surface of the axon fascicle, suggesting that the olfactory Schwann cells were in the initial process of migrating away. On the fourth day when most of the olfactory axons had degenerated, some olfactory Schwann cells were aligned immediately beneath the basal lamina of the olfactory epithelium. These cells were immunopositive for the S-100 protein and possessed an expanded perinuclear space. Many olfactory Schwann cells were present in the region beneath the cribriform plate, while some appeared to have passed through the gaps between the bony plates to reach the olfactory bulb. Hence, the results showed that many olfactory Schwann cells migrated towards the olfactory bulb following loss of axonal contact. Furthermore, on the seventh day following zinc sulfate treatment, some olfactory Schwann cells in the vicinity of the olfactory bulb appeared phagocytic, as indicated by their extension of processes around fragments of cell debris and the presence of lysosome-like organelles in the perikaryon. The control mice which had been intranasally irrigated with saline did not demonstrate massive olfactory axonal degeneration, and the morphology of the nasal cavity region was similar to that of normal mice.