SUBEPENDYMAL CELLS PROVIDE A FASTER RESPONSE TO EPENDYMAL INJURY THAN ASTROCYTES IN THE HYDROCEPHALIC BRAIN

Obstructive hydrocephalus was induced in 12-day-old rats by the infusion of kaolin into the cisterna magna. After 7 days, cortical and ependymal lesions were made with thin wire in non-hydrocephalic brains and in hydrocephalic brains. The wounds were allowed to heal for times ranging from 1 day to 10 days post-lesion, after which the animals were perfused and the brains prepared for histology. Paraffin sections of brain containing the ependymal wound were reacted for glial fibrillary acidic protein by the avidin biotin complex technique. Subependymal cells were associated with the ependymal defect from 1 day in both non-hydrocephalic and in hydrocephalic brains. Reactive astrocytes were identified in hydrocephalic wounded brains on day 3. It was not until day 6 that astrocytes and astrocytic processes were seen in association with the subependymal cells at the wound edge, and astrocytic processes were noted along the needle track in the cortex. The results suggest that the extremely rapid response of subependymal cells to ependymal injury is a mechanism distinct from the astrocytes response for repair in the brain.