Formation of microglia-derived brain macrophages is blocked by adriamycin.

Injection of ricin, the toxic lectin from Ricinus communis, into the rat facial nerve leads to rapid degeneration of motor neurons and concomitant proliferation and transformation of endogenous microglia into brain macrophages. Using [3H]-thymidine autoradiography, immunocytochemistry for microglial markers and electron microscopy, we could show that when ricin was administered together with the cytostatic drug adriamycin, the retrogradely transported adriamycin inhibits the macrophage response induced by toxic ricin. It is concluded that under conditions of neuronal degeneration, e.g., following ricin intoxication, brain macrophages are predominantly, if not exclusively, derived from endogenous microglia.