Plasmalemma-bound nucleoside diphosphatase as a cytochemical marker of central nervous system (CNS) mesodermal cells

Nucleoside diphosphatase (NDPase) activity, using inosine-5'-diphospbate (IDP) as a substrate, was studied by light and electron microscope cytochemistry in brain and spinal cord of normal mouse. After cytochemical incubation for the enzyme, neurons, astroglial and oligodendroglial cells contained reaction product in the cisternae of endoplasmic reticulum (ER) and/or in the trans elements of the Golgi apparatus. In contrast, reaction product for NDPase was concentrated on the outer surface of the plasmalemma of microglial cells, endothelial cells of microvessels, pericytes, and smooth muscle cells of the arteriole wall. An occasional microglial cell contained sparse reaction product in the flattened saccules of the Golgi apparatus. The pattern of enzyme distribution for these cell types was the same for all parts of the nervous system examined in this study. These data suggest that in cells of ectodermal origin, NDPase is intracellular in location, whereas in cells of mesodermal origin, this enzyme is bound to the plasmalemma. The usefulness of this cytochemical reaction for NDPase as a marker of microglial and other cells in brain pathology is discussed.