Absence of mRNA encoding estrogen receptor in the rat cochlea.

Based on changes in hearing thresholds and tinnitus that are co-related with the menstrual cycle, it has been suggested that the cochlea may respond directly to estrogen. For this to occur, the cochlea should express estrogen receptors. In situ mRNA hybridization was performed on normal female rat cochleas, using radiolabeled RNA probes complementary to mRNA encoding estrogen receptor, to determine whether estrogen receptors are present in the cochlea. Strong hybridization of the riboprobes to sections of uterus and hypothalamus indicated that the technique detected estrogen receptor mRNA. No hybridization to any cochlear tissues was observed. The results indicate that estrogen receptors are not expressed on cochlear cells, at least in rats. This in turn suggests that variation in cochlear responses during the estrus cycle are not the result of the direct effect of estrogen on the cochlea. Such variation may, however, be caused by systemic changes in fluid regulation induced by estrogen receptors at a distant site, or by other hormone receptors.