Repair of the ependyma in hydrocephalic brains.

Hydrocephalus was induced in 12-day-old rats by the cisternal infusion of concentrated kaolin suspension. At 19 days of age, a lesion, 100 or 150 microns in diameter, was made in the ependymal lining of the lateral ventricles. Animals were killed at intervals from 1 h to 20 days after the lesion was made. The damaged area was examined by scanning electron microscopy, light and transmission electron microscopy. Between 1 h and 48 h the hole was still open. Small round cells, identified as free subependymal cells, were associated with the edges of the hole from 1 h after the lesion was made. From 48 h, the lesion was completely covered with cell bodies and their processes and no hole was present. Signs of differentiation were seen in the free subependymal cells from 4 days, the cells becoming more electron lucent. By 15 days, three types of cell arrangement were seen within the damaged area: 1 clusters of small cells, with few processes, resembling subependymal cells; 2 small numbers of cells with flat cytoplasmic processes which formed the lining of the ventricular wall; 3 clusters of cells with long thin processes attached to the surface of the ventricular wall but not forming the ependymal lining. The results of this study suggest that, in the hydrocephalic brain, ependymal damage and the repair of a defect within the ventricular wall is initiated by subependymal cells.