Distribution of ferritin in the cerebral cortex of the mouse revealed by electron microscopy

In the cerebral cortex of the mouse, ferritin, administered intravenously or intraperitoneally, readily passes from blood to brain. It is observed to enter the neuropil in an apparently nonspecific manner and is found free in the cytoplasmic ground substance of astrocytes and other cells adjacent to the capillary basement membrane. Its passage through the neuropil appears to occur with water from one cell to another and is not restricted to astrocytes, other cell species, or extracellular space. The data presented suggest that ferritin may specifically activate cell membranes and induce an uptake of molecular species similar to, but more rapid than, that accomplished by pinocytosis.