Response of olfactory ensheathing cells to the degeneration and regeneration of the peripheral olfactory system and the involvement of the neuregulins

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Abstract
In this study we examined the proliferative response of olfactory ensheathing cells (OECs) to olfactory receptor neuron injury induced by zinc sulfate (ZnSO4) irrigation and related the response of OECs within the peripheral system to the inflammatory response induced by injury and the expression profile of neuregulins. After ZnSO4 treatment, degeneration in the epithelium is reproducible and rapid, with regeneration following after 4 days, and is morphologically complete by 5 weeks. Changes in the olfactory bulb are less dramatic, although degeneration of both the outer and the glomerular layers occurred. Treatment also induced a marked inflammatory response in both the epithelium and the bulb. Unlike Schwann cell changes associated with Wallerian degeneration, OECs did not proliferate or obviously migrate within the olfactory system in response to axonal loss, suggesting that the new nerves generated from the epithelium regrow back through conduits already formed by the glia. Expression of neuregulin 1α was maintained in the nerve by OECs, and changes in neuregulin 1 mRNA and erbB2 mRNA expression were detected, indicating that these growth factors may play a role in the regeneration of the peripheral olfactory system but not in OEC proliferation. J. Comp. Neurol. 470:50–62, 2004.