STRUCTURE AND COMPOSITION OF STEREOCILIA CROSS-LINKS IN NORMAL AND HYDROPIC COCHLEAS OF THE GUINEA-PIG

Structure and composition of stereocilia cross-links were investigated cytochemically in normal and hydropic cochleas of the guinea pig. The electron-dense markers colloidal thorium and cationized ferritin were used for visualization. Side links as well as tip links were visualiz ed using both markers. Cationized ferritin allowed a better visualizat ion of the delicate cross-link substructure than did colloidal thorium . Following digestion with neuraminidase, cross-link reactivity for co lloidal thorium was virtually abolished. However, the basic structure of the cross-links could still be observed as a result of routine post -fixation and contrast staining. In both 3- and 6-month hydropic cochl eas glycocalyx reactivity of the stereocilia appeared to be unaltered, provided that stereocilia were still present. However, loss of cross- links of the outer hair cells - resulting in disarrangement of the ste reociliary bundles - was observed in hydropic cochleas. Our results su ggest that cross-links are a separate morphological and cytochemical e ntity, which is different from the glycocalyx. Furthermore, loss of st ereocilia cross-links, with concomitant disarrangement of the outer ha ir cell stereociliary bundle, appears to be one of the early pathologi cal features of surgically induced endolymphatic hydrops, which might be responsible for permanent sensorineural hearing loss.