Cochlear Distribution of Na,K-ATPase and Corticosteroid Receptors in Two Mouse Strains with Congenital Hearing Disorders

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Abstract
As corticosteroid hormones, via their receptors, and Na,K-ATPase are thought to be involved in the regulation of endolymph production, two mouse models were used to investigate whether degeneration of the stria vascularis (SV) and disturbed endolymph composition are correlated with changes in the amounts and distribution of corticosteroid receptors and Na,K-ATPase in the cochlea. Both the shaker-2 mouse and the newly discovered mix mouse are deaf at birth and show vestibular dysfunction. In both mouse strains, the SV is degenerated and endolymph production is severely disturbed. In the shaker-2 mouse, using the C57Bl mouse as a normal control, immunohistochemical staining of mineraloand glucocorticoid receptors (MR and GR) and the Na,K-ATPase subunits f 1 , f 3 and g 1 showed a weaker reaction in all structures of the cochlea. The inner ear morphology of the mix mouse is described and compared to that of asymptomatic littermates. Immunostaining of MR, GR and the different Na,K-ATPase subunits in this mouse was considerably weaker in the SV, while staining intensities were normal in the remaining cochlea. The reduced corticosteroid receptor levels may lead to a reduction in Na,K-ATPase expression in the same tissues, although this conclusion should be treated with caution. The conclusion that reduced Na,K-ATPase levels in both mouse strains may be an important mechanism of the disturbed endolymph production is less controversial.