Hearing Research, 64 (1993) 205-210 © 1993 Elsevier Science Publishers B.V. All rights reserved 0378-5955/93/$06.00 205 HEARES 01847 Tissue specific levels of glucocorticoid receptor within the rat inner ear Kyle E. Rarey, Lisa M. Curtis, Wouter J.-F. ten Cate Departments of Anatomy and Cell Biologyand Otolaryngology, Collegeof Medicine, University of Florida, Gainesville,Florida, USA (Received 22 April 1992; Revision received 17 August 1992; Accepted 21 August 1992) Individual, rat inner ear tissues were isolated and processed for determination of levels of glucocorticoid (GR) receptor by an Enzyme Linked Immuno-Sorbant Assay (ELISA). Differing levels of GR receptor between seven sampled inner ear regions were measured. Levels of GR receptors in the spiral ligament tissues were found to be significantly higher compared to all other tissue samples. GR levels in the tissues of stria vascularis and organ of Corti were different from one another but both were statistically higher than those detected in the vestibular tissue samples (dark cell regions, cristae ampullares and maculae utriculi), which had the lowest GR receptor levels measured. Intermediate levels of GR receptor were found in the endolymphafic sac region. It is suggested that the varying levels of inner ear GR receptors may be indicative of differing biological responses among the given tissues, as well as differences in the magnitudes of such responses to circulating glucocorticoids. Adrenal steroids; Cochlea; Vestibular endorgans; ELISA; BUGR 2 Introduction Action of the adrenal steroids, mineralocorticoids and glucocorticoids, on the inner ear has been a re- search issue of this laboratory in defining mechanisms of regulation of local microhomeostasis within the in- ner ear. Originally, receptors for such hormones were identified in the inner ear of the rat by in vitro binding studies (Rarey and Luttge, 1989). Adrenal steroid re- ceptors were found subsequently in the guinea pig ip.ner ear also by in vitro binding studies (Pitovski et al., 1991, 1992). Both morphological and biochemical parameters have been used to determine whether a correlation existed between levels of circulating adrenal corticosteroids and certain inner ear tissues. Changes in cellular morphology of the stria vascularis and of ampullar dark cells have been observed, and changes in Na,K-ATPase activity of given inner ear tissues have been measured fluorometrically when levels of circulat- ing adrenal steroids have been altered (Rarey et al., 1989a,b, 1991; ten Cate et al., 1990, 1991; Lohuis et al., 1990). Recently, autoregulation of the glucocorticoid (GR) receptors in the rat inner ear was investigated using tissues of the lateral cochlear wall, by ELISA (Rarey et al., 1992). The GR receptors were found to be dynamic Correspondence to: Kyle E. Rarey, P.O. Box 100235, J. Hillis Miller Health Center, Department of Anatomy and Cell Biolo~, University of Florida, Gainesville, FL 32610, USA. Fax: (904) 392-3305. and responsive to differing levels of circulating gluco- corticosteroids. During the execution of that study, the lateral wall tissues were subdivided further into spiral ligament and stria vascularis since previous morpholog- ical and biochemical studies focused on these individ- ual tissues (Rarey et al., 1989a,b, 1991; Lohuis et al., 1990). Interestingly, it was observed that GR receptor levels were higher in the spiral ligament than in the stria vascularis, and that the response of the GR recep- tors in each tissue region to varying concentrations of GR was tissue-specific (Rarey et al., 1992). To further define if levels of GR varied among other inner ear tissues, the objective of this investiga- tion was designed to sample seven inner ear tissues, including both sensory and nonsensory regions, and to compare GR levels of each tissue with one another. The importance of studying inner ear GR receptors is based upon the following facts. First, certain inner ear dysfunctions have been associated with adrenal steroid disorders (Liston and Meyerhoff, 1987; Pulec, 1984; Goldman, 1962). Secondly, clinical management of se- lect inner ear dysfunctions, e.g., sudden hearing loss, Meniere's disease, autoimmune-induced hearing loss, includes steroid therapy with glucocorticoid-acting agents (Goldman, 1962; Morrison, 1975; Schiff and Brown, 1974; Wilson et al., 1980; Johnson et al., 1992; Hackett et al., 1988). Thirdly, since local homeostasis of ions and fluids within the inner ear membranous labyrinth has been conjectured to be under neuroen- docrine regulation (Anniko and Wroblewski, 1986; Rarey and Luttge, 1989; Rarey et al., 1991), GR may