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We performed an immunohistochemical investigation of the distribution of glucocorticoid receptors (GRs) in the murine inner ear and found that GRs were expressed extensively, but with various degrees of immunoreactivity in different regions. We observed the strongest GR expression in the type III fibrocytes of the spiral ligament. Although the immunoreactivity of the cochlear hair cells and of the vestibular sensory epithelia was weak, the neighboring cochlear supporting cells and the subepithelial regions of the vestibular sensory epithelia were immunostained. Staining for GRs was also positive in the spiral ganglia and vestibular ganglia, as well as in the endolymphatic sac. The role of GRs in the inner ear is discussed.

The distribution of Na+, K(+)-ATPase, Ca(++)-ATPase, carbonic anhydrase, and calcium-binding proteins were investigated immunohistochemically in paraffin sections of guinea pig inner ears. Marginal cells of the stria vascularis, type II fibrocytes of the spiral ligament, and cells in supralimbal and suprastrial regions, were positive for Na+, K(+)-ATPase. Type I fibrocytes of the spiral ligament were positive for Ca(++)-ATPase, carbonic anhydrase, calmodulin and osteopontin. In the vestibular system, dark cells were positive for Na+, K(+)-ATPase. However, these cells and subepithelial fibrocytes were negative for Ca(++)-ATPase, carbonic anhydrase, and the calcium-binding proteins. In the endolymphatic sac, epithelial cells in intermediate and distal portions were positive for Na+, K(+)-ATPase, but the reaction was less than that in the stria. The same endolymphatic sac cells that were positive for Na+, K(+)-ATPase were also positive for Ca(++)-ATPase and calcium-binding proteins, but negative for carbonic anhydrase. The presence of Ca(++)-ATPase and calcium-binding proteins in the type I fibrocytes of the spiral ligament suggests that these cells are involved in mediating Ca++ regulation. Lower levels of Na+, K(+)-ATPase and the co-existence of Ca(++)-ATPase and calcium-binding proteins in the epithelial cells of the endolymphatic sac indicate that these cells have a distinctive role in ion transport that is different from that of the cells of the stria vascularis and vestibular dark cells.

A quantitative analysis of immunocompetent cells in the middle ear mucosa of mice was carried out by an indirect immunostaining method using various monoclonal antibodies. Mice bred in germ-free, specific pathogen-free, and conventional conditions were used to examine nonimmunized middle ear mucosa. Middle ear mucosae of otitis media-induced mice were also examined. In normal middle ear mucosa, mast cells were substantial, followed by Mac-1-positive cells and lymphocytes. Even though IgA-, IgM-, and Lyt-1-positive cells were seen in the mucosa of conventional mice, IgM-positive cells were seen only in mucosae of specific pathogen-free and germ-free mice. In otitis media-induced mice by inoculation with nontypable Haemophilus influenzae or lipopolysaccharide, Mac-1-positive cells were dominant. Although the numbers of IgM- and Lyt-1-positive cells increased markedly, the numbers of other lymphocyte subsets did not increase until 14 days after inoculation. These findings suggest that the middle ear is immunologically a potential organ as long as it is not exposed to antigenic stimulation. It is considered to be an immunoreactive site only after it has been activated with pathogens.

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