Absence of mRNA encoding estrogen receptor in the rat cochlea

Based on changes in hearing thresholds and tinnitus that are correlated wit h the menstrual cycle, it has been suggested that the cochlea may respond d irectly to estrogen. For this to occur, the cochlea should express estrogen receptors. In situ mRNA hybridization was performed on normal female rat c ochleas, using radiolabeled RNA probes complementary to mRNA encoding estro gen receptor. to determine whether estrogen receptors are present in the co chlea. Strong hybridization of the riboprobes to sections of uterus and hyp othalamus indicated that the technique detected estrogen receptor mRNA. No hybridization to any cochlear tissues was observed. The results indicate th at estrogen receptors are not expressed on cochlear cells, at least in rats . This in turn suggests that variation in cochlear responses during the est rus cycle are not the result of the direct effect of estrogen on the cochle a. Such variation may, however, be caused by systemic changes in fluid regu lation induced by estrogen receptors at a distant site, or by other hormone receptors.