Reactions of S-100-positive glia after injury of mouse cerebral cortex

Reactions of glial cells after stab wounding of mouse cerebral cortex were studied by [3H]thymidine autoradiography combined with immunohistochemistry for S-100 protein. S-100-positive cells in the stabbed cortex had the light and electron microscopic characteristics of astrocytes, and they showed remarkable hypertrophic changes 4 to 5 days after stabbing. There were many cells labeled with [3H]thymidine in the stabbed cortex from 24 h to 8 days after stabbing, and the number of labeled cells was maximum at 48 h. A few of the labeled cells were S-100-positive, and the labeled S-100-positive cells were seen 24 h to 6 days after stabbing, mostly after 72-96 h. By successive injections of [3H]thymidine for 6 days after stabbing, about 90% of labeled cells were S-100-negative, and about 90% of S-100-positive cells were unlabeled with [3H]thymidine. The increase in number of S-100-positive cells by day 6 after stabbing was not statistically significant (P greater than 0.05). These results suggest that reactive proliferation of astrocytes is a minor phenomenon in gliosis of injured cerebral cortex, in contrast with their remarkable reactive hypertrophy.