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 b y means of combined in vivo bromodeoxyuridine (BrdU) administration an d immunohistochemical demonstration of glial fibrillary acid protein ( GFAP), vimentin, Ricinus communis agglutinin 120 (RCA-1), Griffonia si mplicifolia B4 isolectin (GSI-B4), keratan sulphate (KS), carbonic anh ydrase C (CA.C), transferrin (TF) and ferritin. Two days after the inj ury, 7.5% of the proliferating cells were GFAP-positive reactive astro cytes, 5.7% were RCA-1-positive cells and 17.4% were GSI-B4-positive c ells. Lectin-binding cells had the microscopic and ultrastructural asp ects of microglia; they proliferated around the needle track and in th e corpus callosum. Microglia represented a large fraction of the proli ferating cells. Evidence is presented for the origin of at least a pro portion of perilesional astrocytes and microglia from the periventricu lar matrix, and of microglia from blood precursors. Other non-prolifer ating 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 necr osis.