Age-related morphological changes in the basement membrane in the stria vascularis of C57BL/6 mice

Basement membrane anionic sites (BMAS) are involved in the selective transport of electrically charged macromolecules in cochlear capillaries. Using cationic polyethyleneimine (PEI), we examined age-related changes in BMAS in the cochleae of C57BL/6 mice. The mice were grouped according to age as follows: 3 days, 4 weeks, 8 weeks, 6 months, and 12 months. In the right bony labyrinths, widths of the stria vascularis were measured in paraffin-embedded sections using light microscopy. The left bony labyrinths were immersed in a 0.5 % cationic PEI solution and embedded in epoxy resin. Ultrathin sections of the left cochlea were examined using transmission electron microscopy. A significant difference in stria vascularis width was observed between the 4-week-old and 12-month-old mice. The PEI distribution in the capillary and epithelial basement membranes (BMs) of the cochlea was observed. In all animals, PEI particles were evenly distributed in the capillary BM of the spiral ligament and in the subepithelial BM of Reissner's membrane. In the stria vascularis, PEI particles were evenly distributed in the capillary BM in 3-day-old mice. In 4- and 8-week-old mice, PEI particle sizes were markedly lower than those observed in 3-day-old mice. In 6- and 12-month-old mice, PEI particles were hardly detected in the strial capillary BM. In the strial capillary BM in these mice, the laminae rarae externa and interna disappeared, but the lamina densa became larger. We speculated that age-related changes of strial capillary BMAS may affect electrically charged macromolecule transport systems in the stria vascularis of C57BL/6 mice.