Initial response of silver-impregnated "resting microglia" to stab wounding in rabbit hippocampus

Adult rabbits received stab wound in the cerebrum and were sacrificed at intervals of 20, 30, and 39 h thereafter. Each animal was injected intracerebrally with 3H-thymidine 2h before fixation. Altered brain tissues of the stratum radiatum of hippocampus were taken for examination. Response of "resting microglia" to stab wounding was investigated by electron microscopic autoradiography and by autoradiography applied on silver-impregnated materials. Following results were obtained: (1) Resting microglia undergo marked swelling shortly after the brain damage. We designate these cells as "swollen microglia". (2) Swollen microglia form the only cell population that proliferate actively in the initial stage of glial response to the brain injury, and (3) astroglia do not proliferate during the same experimental periods, in the rabbit hippocampus.