Reactive cell proliferation and microglia following injury to the rat brain.

The non-astrocytic cells which proliferate in the rat brain after the induction of an area of necrosis have been characterized and counted by means of combined in vivo bromodeoxyuridine (BrdU) administration and immunohistochemical demonstration of glial fibrillary acid protein (GFAP), vimentin, Ricinus communis agglutinin 120 (RCA-1), Griffonia simplicifolia B4 isolectin (GSI-B4), keratan sulphate (KS), carbonic anhydrase C (CA.C), transferrin (TF) and ferritin. Two days after the injury, 7.5% of the proliferating cells were GFAP-positive reactive astrocytes, 5.7% were RCA-1-positive cells and 17.4% were GSI-B4-positive cells. Lectin-binding cells had the microscopic and ultrastructural aspects of microglia; they proliferated around the needle track and in the corpus callosum. Microglia represented a large fraction of the proliferating cells. Evidence is presented for the origin of at least a proportion of perilesional astrocytes and microglia from the periventricular matrix, and of microglia from blood precursors. Other non-proliferating microglia cells transiently appeared in the normal brain around the wound, in agreement with the existence of two different microglia cell populations reacting with different modalities to an area of necrosis.