AGE-RELATED THICKENING OF BASEMENT-MEMBRANE IN STRIA VASCULARIS CAPILLARIES

Ultrastructural examination was undertaken to investigate the pathogen esis of age-related atrophy of the stria vascularis (StV). Basement me mbrane (BM) thickness was increased in 65-85% of strial capillaries in gerbils aged 33 months or older and often exceeded by several-fold th at observed in young controls. In an early stage of thickening the BM expanded slightly around the full capillary profile, after which nodul ar expansions of BM encircling slender cell processes were often obser ved at or near one or both poles of the elliptical vessel profile. As widening progressed, the BM consisted of 2-3 layers separated by cell processes in the nodules but fewer strata elsewhere. Association of sl ender processes of both endothelial cells and pericytes with focal thi ckening outside the process suggested their participation in genesis o f the capillary lesion. In later stages of atrophy, pericytes degenera ted and disappeared, while endothelial cells remained intact. Eventual ly, thick multilayered BM devoid of endothelial cells surrounded a nar row lumen occluded by debris. The age-related change in BM in the inne r ear was confined to StV capillaries. Degenerative changes in StV epi thelial cells occurred apparently as a secondary consequence of the ca pillary lesion. The pathologic alterations in marginal cells included extrusion of blebs from the luminal surface, separation and loss of ba solateral interfoldings, alteration and depletion of mitochondria and nuclear pyknosis. At the end-stage of degeneration, the StV consisted of a simple or multiple layer of squamous cells lining the scala media .