Development of blood-labyrinth barrier in the semicircular canal ampulla of the rat

Cationic polyethyleneimine (PEI) administered intravenously was transported to anionic sites on the capillary and subepithelial basal laminae (BL) in the vestibular labyrinth. Therefore, changes in the PEI distribution on the BL reflect changes in the transport system in the vestibular labyrinth. A 0.1% PEI solution was administered intravenously (7.5 ml/kg) to developing (1, 4, 7, 14 days after birth) and adult rats in order to investigate the development of the macromolecular transport in the ampulla of the semicircular canal as a function of age. After 1 h, the bony labyrinth was removed and embedded in Epoxy resin. Ultrathin sections of the ampulla were then examined with a transmission electron microscope. In the subepithelial BL in the dark cell area and capillary BL in the crista ampullaris, the PEI distribution in both 1- and 4-day-old rats was markedly increased compared to that in either 7-, 14-day or adult rats. In the sensory cells in 1-, 4-day or 7-day-old rats, PEI density and area was significantly greater than in the adult rats. These findings suggest that the macromolecular transport system in the developing rat ampulla becomes mature by 14 days after birth and that the maturation of its transport system in the ampulla is strongly associated with that in the stria vascularis.