PHAGOCYTIC RESPONSE IN PHOTOCHEMICALLY INDUCED INFARCTION OF RAT CEREBRAL-CORTEX - THE ROLE OF RESIDENT MICROGLIA

Background and Purpose In this study we assessed the relative extent t o which resident microglia and blood-borne macrophages contribute to t he population of phagocytes after focal infarction of the rat cortex. Methods Focal cerebral infarction was induced in rats by photothrombos is after hematogenous macrophages were depleted by means of liposomes containing dichloromethylene diphosphonate. The phagocytic activation of microglia and macrophages was monitored by immunocytochemistry with the antibody ED1. Results In both macrophage-depleted rats and contro ls, ED1+ phagocytes bordered the infarct to the same extent at day 3 a fter photothrombosis. By contrast, at day 6 after photothrombosis ED1 phagocytes in control rats greatly outnumbered those in macrophage-de pleted rats. With the use of the antibody 0x42 directed against the CR 3 receptor on the surface of microglia, it was possible to selectively document the transition of resident microglia into stellate and amebo id phagocytic microglia during the first 6 days after photothrombosis in the absence of blood-borne macrophages. Conclusions The initial pha gocytic response after focal brain ischemia is an intrinsic property o f the nervous system mainly performed by resident microglia. The major ity of hematogenous macrophages are recruited secondarily to participa te In the removal of necrotic tissue.