Distribution of glucocorticoid receptors and 11 beta-hydroxysteroid dehydrogenase isoforms in the rat inner ear.

11β-hydroxysteroid dehydrogenase (11β-HSD) is an enzyme complex responsible for the conversion of hormonally active cortisol to inactive cortisone, and two isoforms of the enzyme (11β-HSD1 and 11β-HSD2) have been cloned and characterized. An immunohistochemical study was performed to determine the precise distribution of glucocorticoid receptors (GRs) and the isoforms of 11β-HSD in the rat (postnatal day 1, 4, 10, and adult). Immunoreactivity of GRs was detected in the stria vascularis (SV), the outer hair cells (OHCs), the inner hair cells (IHCs), the spiral ligament (SLig), the spiral limbus (SLib), the spiral ganglion cells (SGCs), Reissner's membrane (RM), the cochlear nerve (CN), the vestibular hair cells (VHCs), the dark cells (DCs), and the vestibular nerve (VN) in the rats. Immunostaining of 11β-HSD1 was observed in almost all the tissues in the cochlea and the vestibule except SLig, SLib, SGCs, CN, VHCs, and VN during all developmental stages, whereas, immunoreactivity of 11β-HSD2 was not detected in any of the inner ear tissues. A polymerase chain reaction (PCR) study was also performed on GRs, 11β-HSD1, and 11β-HSD2 in the OC, SV and vestibule of the postnatal rats, and revealed that mRNAs were detected in all those and tissues in all the developmental days of postnatal days 1, 4, and 10. This data indicates that expression of GRs and 11β-HSD isoforms in the inner ear is tissue and age-specific, and that different local steroid regulation by GRs and the isoforms of 11β-HSD is present in each part of the inner ear.