Electron Microscopic Study on the Amoeboid Microglial Cells in the Roof Plate of the Early Chick Embryo Brain

The amoeboid microglial cells (AM cells), which were acid phosphatase-positive histochemically, present in the rhombencephalon coated with the leptomeninges of the 8-day incubation chick embryos were investigated by electron microscopy. It was found that the AM cells occurred simultaneously in the leptomeninges, in the roof plate, and in the ventricle. Considering the distribution of the cell in these three sites along with the present author's earlier findings of ACPase reactions for the AM cells, it is highly probable that in the rhombencephalon the AM cells originate from the leptomeninges and then enter the ventricle through the roof plate.