Elongated pericyte-like cells connect discrete capillaries in the cochlear stria vascularis of gerbils and rats

Bridging structures between discrete capillaries in the stria vascularis of the cochlea were studied morphologically in gerbils and rats. Serial thin sections for transmission electron microscopy revealed (1) that elongated cells surrounded by the basal lamina provided the structural basis for the bridging structure, (2) that the basal lamina surrounding the elongated cell extended to the basal lamina around the capillary endothelial cell, (3) that the electron density of the cytoplasm was similar to that of the pericytes around the capillaries, and (4) that the cell was attached to the capillaries at both ends only. Visualization of the basal lamina by immunofluorescent methods revealed (1) that capillaries were often bent at the site of attachment of the bridging cell, (2) that the bridging cell bifurcated occasionally, and (3) that the density of the bridging cell was much higher in the stria vascularis than in the underlying spiral ligament. Filamentous actin visualized by fluorescent phalloidin was not apparent in the bridging cell. We propose that the bridging cell provides mechanical strength to the tortuous capillary network in the stria vascularis and participates in the specific function of the stria vascularis in cooperation with other types of cells.