Experimental intracerebral movement of electron microscopic tracers of various molecular sizes.

The authors demonstrate that, while the intracerebral movement of proteins and other relatively large molecules is restricted by tight junctions of endothelia and epithelia of the brain, calcium ion penetrates these barriers and moves between the blood and CSF cavities by extracellular pathways. Mechanisms underlying CSF formation are considered on the basis of this anatomical continuity of the vascular, extracellular, and CSF compartments of the brain for very small molecules.