A scanning and transmission electron microscopic study of amoeboid microglial cells in the prenatal rat brain following a maternal injection of 6-aminonicotinamide.

The amoeboid microglial cells in the cavum septum pellucidum of prenatal rats aged 22 days post-conception were studied by scanning and transmission electron microscopy. The cells in normal rats had numerous filopodia, while those in experimental animals whose mothers had received an intraperitoneal injection of 6-aminonicotinamide (6-AN) on the 14th day of gestation, showed an abundance of blebs or possessed smoother contours. Extravasated red blood cells and nerve fibres were seen to be engulfed by the amoeboid cells of the blebbed as well as the smooth type. Transmission electron microscopy confirmed the phagocytosis of red blood cells and nerve fibres in the cytoplasm of the amoeboid cells. It is postulated that the amoeboid microglial cells responded to 6-AN by increasing their phagocytic activity and by changing their surface morphology. The factors leading to such alterations are discussed.