GLUCOCORTICOID RECEPTOR EXPRESSION IN THE POSTNATAL RAT COCHLEA

The glucocorticoid receptor (GR) expression in the neonatal rat cochlea was investigated by utilization of a polyclonal antibody against GR, the immunoreactivity of which exhibited a distinct, age-dependent developmental pattern in tissues of the spiral ligament (SL). Immunostaining of GR appeared initially at the 7th postnatal day (PND), increased rapidly between the 14th and 21st PND, and reached adult-like expression levels by the 21st PND. Less pronounced, developmentally regulated expression patterns of GR were observed in cells of the spiral limbus (SLi), spiral ganglion (SG), organ of Corti (OC), and cochlear nerve (CN). For example, high expression levels of GR were observed in the SLi, SG and OC at 3 PND; subsequently, GR immunoreactivity levels decreased from 7 to 14 PND, and then GR immunoreactivity intensified in these regions by 21 PND. No remarkable changes in GR expression were observed in stria vascularis (SV). These data indicate that GR expression in the inner ear is tissue and age-specific, and that GR expression parallels both Na,K-ATPase expression and endocochlear potential development.