Distribution of anionic sites and glycoconjugates on the endothelial surfaces of the developing blood-brain barrier

The distribution of anionic sites detected in vitro with cationized ferritin and lectin-binding sites on the endothelial cell (EC) surface of brain micro-blood vessels was studied by electron microscopy. Gold-labeled lectins and glycoproteins and Lowicryl K4M-embedded brain samples obtained from mouse embryos (19th day), and from 1-, 5-, 12-, 24- and 48-day-old and adult mice were used. It was shown that the functional maturation of the blood-brain barrier (BBB) occurring in the mouse after birth between the 12th and 24th day of life is accompanied by a disappearance of vesicular transport in capillaries and by the formation of a uniform, thin, negatively charged layer on the surface of the EC. Concomitantly the binding of lectins specific for beta-D-galactosyl (RCA) and sialyl (LFA and WGA) residues become progressively more intense and uniform on both luminal and abluminal fronts of the EC. The concentration of HPA-binding sites on the abluminal side of the EC and in the basement membrane increases. Similarly the binding of Con A becomes more intense on abluminal than on luminal front of the EC. These observations suggest that extensive remodeling of anionic sites and surface glycoprotein layer and also the elaboration of ECs polarity occur during BBB maturation.