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

The MRL-Fas(lpr) mouse, a model of multisystemic, organ nonspecific autoimmune disease, has been proposed as a model of immune-mediated inner ear disease. A preliminary study employing light microscopy indicated that it develops cochlear pathology that appeared most striking in the stria vascularis, where cells underwent edema and degeneration. However, other structures, including the inner and outer hair cells and the supporting cells, also appeared to display pathology. The current study analyzed cochlear ultrastructure using transmission electron microscopy to better delineate the cochlear lesions found in these animals. MRL-Fas(lpr) animals were allowed to develop systemic disease (20 weeks old) and then had auditory brainstem response (ABR) thresholds determined. Animals were then killed and their cochleas prepared for electron microscopy. Age-matched MRL-+/+ and BALB/c mice served as controls. Results indicated that MRL-Fas(lpr) mice demonstrated elevated ABR thresholds. In contrast to a preliminary report, the cochlear pathology was observed exclusively in the stria vascularis, where cells demonstrated 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(lpr) mouse develops cochlear abnormalities focused in the stria vascularis. Whether the mechanism of the cellular degeneration involves autoimmune, genetic, or uremic processes has yet to be determined.