Proliferation of microglia in the injured cerebral cortex of mice as studied by thiamine pyrophosphatase histochemistry combined with 3H-thymidine autoradiography.

Abstract

Proliferation of microglia in the mouse cerebral cortex around a stab wound was studied, using thiamine pyrophosphatase (TPPase) histochemistry combined simultaneously with 3H-thymidine (3H-TdR) autoradiography. Many cells with cell membrane TPPase activity (TPPase-positive cells) were scattered in the cortical parenchyma apart from the stab wound. Light and electron microscopically, TPPasepositive cells were identified as microglia but not as astrocytes, oligodendrocytes, or neurons. TPPasepositive cells were immunohistochemically negative for astrocytic markers, i. e., S-100 protein and glial fibrillary acidic protein. Autoradiography showed that approximately 92% of all cells labeled with 3H-TdR within 2 days after stab-wounding were TPPase-positive cells. Approximately 60% of all labeled cells 3 and 4 days after stab-wounding were also TPPase-positive cells. These results suggest that microglia, but not astrocyte, begins active proliferation immediately after injury and is the major cell type having high proliferative activity in the injured cerebral cortex.