Effects of age and sex on the expression of estrogen receptor α and β in the mouse inner ear

Conclusion: Estrogen receptor (ER) alpha and beta were expressed in the inner ear, and expression decreased with increasing age. ER alpha may alter cochlear and vestibular sensory transduction, and ER beta may have a neuroprotective function in the inner ear. Objective: Expression of ER alpha and ER beta in the mouse inner ear and its alterations with sex and aging were analyzed. Materials and methods: Male and female CBA/J mice aged 8 weeks and 24 months were used. The localization and the intensity of ER alpha and ER beta immunoreactivity in the inner ear of young and old mice of both sexes were investigated by immunohistochemistry. Results: ER alpha and ER beta were co-expressed in the inner ear, i.e. in the nuclei of stria vascularis, outer and inner hair cells, spiral ganglion cells and vestibular ganglion cells, vestibular dark cells and endolymphatic sac. Strial marginal cells, outer hair cells and type II ganglion cells showed less expression of ER alpha. No gender-or age-related difference was noted in the expression pattern of ER alpha or ER beta but fluorescence intensity of ER alpha was stronger in young female mice than in voting male mice. In contrast, ER beta revealed no significant difference. In the old mice, fluorescence intensities of both ER alpha and ER beta were significantly decreased in both sexes.