Morphological studies on neuroglia. III. Macrophage response and "microgliocytosis" in kainic acid-induced lesions.

Light- and electron-microscopic investigations of kainic acid-induced lesions revealed a marked macrophage response and "microgliocytosis". The hematogenous origin of reactive elements, such as brain macrophages and "'microglia-like reactive cells", was demonstrated when blood phagocytes were labeled with carbon particles or horseradish peroxidase prior to induction of the kainic acid-lesion. The induced lesion showed a proliferation of microglial cells, which led to a state of "microgliocytosis" in the later stage of lesioning. Since it is now generally accepted that microglial cells in the state of "microgliocytosis" are derived from the "microglia-like reactive cells", proliferated microglial cells in the brain lesions are probably of hematogenous origin. The relationships among the brain macrophages, the "microglia-like reactive cells" and the intrinsic microglial cells are discussed.