Light and electron microscopic demonstration of some lysosomal enzymes in the amoeboid microglia in neonatal rat brain.

A cytochemical study of the amoeboid microglial cells in the brain of the neonatal rat has shown that these vacuolated cells exhibit strong acid phosphatase, aryl sulphatase and adenosine triphosphatase (ATPase) activities. Endogenous peroxidase, however, was not present. With the electron microscope the reaction product of acid phosphatase was found to be localized in some of the Golgi cisternae, in the majority of the electron-dense secretory granules, and in an occasional long tubular profile. The secretory granules were not uniformly stained for this enzyme, some showing only a focal reaction or none at all. The distribution of the activity of aryl sulphatase corresponded to that of acid phosphatase except that all the granules appeared to contain the former enzyme. With the light microscope the amoeboid microglial cells were intensely stained for ATPase. From these observations it was concluded that amoeboid microglia are active phagocytes and their enzyme-rich secretory granules are lysosomes.