Nascent microglia in the developing brain.

Nascent microglia cells in the developing brain were studied by morphological, cytochemical, and autoradiographic methods. These cells are a well differentiated population, characterized by the presence of an activated nucleus, numerous ribosomes, a well developed Golgi system and associated structures including clear vesicles, dense granules, and membrane-bound polymorphous structures. Big clear vacuoles in the cytoplasm are a constant feature; filaments and microtubules are found in variable numbers. Finger-like projections and invaginations of the plasma membrane are usually found. The identification of these cells with the classical microglial cells stained by Rio Hortega's method was made by reconstruction of 20 cells using serial sections. These cells show strong NADPH dehydrogenase, ATPase, and acid phosphatase activities, in addition to nonspecific esterase activity which is inhibited by sodium fluoride. Transfusion of labeled bone marrow cells from a donor showed labeled cells only in those areas in which nascent microglia cells are more abundant. Taken together, these data suggest an exogenous, most probably monocytic, origin of nascent microglia. New studies with membrane markers are, however, needed for providing better characterization of these cells.

Biosynthesis of myelin and neurotoxic factors in the serum of multiple sclerosis patients.

The in vitro synthesis of myelin proteins has been studied by measuring the incorporation of [3H] lysine in developing rat brain slices. This incorporation system has been used to assay potentially gliotoxic and myelinolytic agents. A reduced incorporation of the labelled amino acid into myelin proteins occurs in the presence of anti-myelin anti-serum and anti-basic protein anti-serum. Diphtheria toxin has been found to inhibit the synthesis of myelin basic and proteolipid protein in the white matter slices of developing rats. Recent experiments with serum samples from multiple sclerosis patients in exacerbation suggest the presence of a factor which interferes with the synthesis of myelin in white matter slices.