The proliferative response of S-100 protein-positive glial cells to injury in the neonatal rat brain.

Astroglial proliferative response to unilateral injury of the cerebral hemisphere was studied in newborn rats using [3H]thymidine autoradiography combined with immunocytochemical staining for S-100 protein as an astroglial marker. The animals received [3H]thymidine at different intervals following injury and the distribution of double-labeled cells was recorded 4 h after each [3H]thymidine injection. The reactive proliferation of all cells within the investigated areas was detectable as early as about 2 h after injury. However, the quantitative increase in astroglial mitotic rate could be first detected on day 1 following the injury and the reactive changes were observed until day 8. They were regarded as evidence for the ability of astroglia to proliferate in response to injury in the neonatal brain. Since the astroglial divisions occurred mainly at the lesion site, the post-traumatic gliosis could be considered not only a result of astrocyte migration towards the lesion but also an effect of local mitotic activity.