Ultrastructural pathology in the stria vascularis of the MRL-Fas(lpr) mouse

The MRL-Fas(1pr) mouse, a model of multisystemic, organ nonspecific autoimm une disease, has been proposed as a model of immune-mediated inner ear dise ase. A preliminary study employing light microscopy indicated that it devel ops cochlear pathology that appeared most striking in the stria vascularis, where cells underwent edema and degeneration. However, other structures, i ncluding the inner and outer hair cells and the supporting cells, also appe ared to display pathology. The current study analyzed cochlear ultrastructu re using transmission electron microscopy to better delineate the cochlear lesions Found in these animals. MRL-Fas(1pr) animals were allowed to develo p systemic disease (20 weeks old) and then had auditory brainstem response (ABR) thresholds determined. Animals were then killed and their cochleas pr epared for electron microscopy. Age-matched MRL-+/+ and BALB/c mice served as controls. Results indicated that MRL-Fas(1pr) mice demonstrated elevated ABR thresholds. In contrast to a preliminary report, the cochlear patholog y was observed exclusively in the stria vascularis, where cells demonstrate d hydropic degeneration. Strial capillary structure was normal as were the rest of the cellular cochlear constituents. No inflammatory infiltrate was noted. These studies confirm that the MRL-Fas(1pr) mouse develops cochlear abnormalities focused in the stria vascularis. Whether the mechanism of the cellular degeneration involves autoimmune, genetic, or uremic processes ha s yet to be determined. (C) 1999 Elsevier Science B.V. All rights reserved.