Structural changes in thestrial blood-labyrinth barrier of aged C57BL/6 mice.

Tight control over cochlear blood flow (CoBF) and the blood-labyrinth barrier (BLB) in the striavascularis is critical for maintaining the ionic, fluid and energy balance necessary for hearing function. Inefficient CoBF and disruption of BLB integrity have long been considered major etiologic factors in a variety of hearing disorders. In this study, we investigate structural changes in the BLB of the striavascularis in age-graded C57BL/6 mice (1 to 21 months) with a focus on changes in two blood barrier accessory cells, namely pericytes (PCs) and perivascular-resident macrophage-like melanocytes (PVM/Ms). Decreased capillary density was detectable at 6 months, with significant capillary degeneration seen in 9- to 21-month-old mice. Reduced capillary density was highly correlated with lower numbers of PCs and PVM/Ms. "Drop-out" of PCs and "activation" of PVM/Ms were seen at 6 months, with drastic changes being observed by 21 months. With newly established in vitro three-dimensional cell-based co-culture models, we demonstrate that PCs and PVM/Ms are essential for maintaining cochlear vascular architecture and stability.