Reactive microglia in the developing brain.

Reactive microglia in the developing brain after stab wound was studied by morphological, cytochemical, and autoradiographic methods. Morphologically, early reactive cells are of the "M" cell type (Matthews 1974). They show an activated nucleus, cytoplasm rich in ribosomes with wide Golgi complex and variable numbers of lipid inclusions. Big clear vacuoles are found in many of these cells. Microtubules not associated with centrioles and filaments may or may not be present. Junctional complexes of the zonula or puncta adherentia types are occasionally found. Strong NADPH dehydrogenase, weak NADH dehydrogenase, strong ATPase, and strong acid phosphatase, in addition to nonspecific esterase activities were demonstrated in many reactive cells. Intravenous infusion of labelled bone marrow cells from a donor showed labelled macrophages and labelled perivascular cells at the site of injury. Intracerebral injection of a small dose of tritiated thymidine at the time of injury resulted in the appearance of labelled macrophages in the following days. These data suggest that many of the reactive cells have an exogenous, more probably monocytic, origin; but a certain amount of endogenous cells also act as macrophages in brain injuries.