Further studies on the identification of microglia in mixed brain cell cultures.

The investigation of brain microglia in primary cultures of dissociated cerebral cortical cells has been continued here utilizing a histochemical procedure for thiamine pyrophosphatase, which selectively stains microglia in whole tissue. This procedure also selectively stained a subpopulation of cells in the cortical cultures. The stained cells were small and exhibited quite variable morphology; from these features, a corresponding cell population could be identified in viable cultures. The stained cells, which were distinct from previously identified macrophage forms, were also distinguished from similar appearing cell types--small neurons and oligodendrocytes. Based on their staining properties, morphology, and distinction from other cell types, the identified cells are proposed as equivalents of ramified microglia.