INCREASED LAMININ DEPOSITION IN CAPILLARIES OF THE STRIA VASCULARIS OF QUIET-AGED GERBILS

The distribution of laminin (LA) and type IV collagen (IV-C) in the ge rbil inner ear was investigated by light and electron microscopic immu nohistochemistry. Changes in protein expression were assessed from bir th to old age to determine the relation of these constituents to matur ation of the cochlea and development of presbyacusis. The distribution of LA paralleled that of IV-C during postnatal development, and both were visualized in the basement membrane (BM) of endothelial, epitheli al and spiral ganglion cells in neonatal and young adult gerbils. Immu nopositive BM underlying the stria vascularis disappeared at 8-12 days after birth coincident with the development and maturation of the str ial capillaries. Immunoreactivity for LA afforded an index to the thic kness of the BM and was found to increase with age only in the BM of s trial capillaries. At 6 months of age, occasional strial capillaries i n the apex of the cochlea showed thickening of the LA-positive BM. Abn ormal deposition of LA in strial capillary BM spread to lower turns an d increased in prevalence with advancing age, affecting apical and bas al more than middle cochlear turns. Thickening of the capillary BM app eared to precede capillary obstruction which eventuated in complete st rial atrophy. Staining for IV-C in the walls of the strial capillaries did not increase with age. The data show that LA and IV-C play import ant roles in postnatal development of the cochlea and that LA depositi on increases with age only in the BM of strial capillaries.