A SYSTEMATIC HISTOCHEMICAL INVESTIGATION IN MAMMALS OF THE DENSE GLYCOCALYX GLYCOSYLATIONS COMMON TO ALL CELLS BORDERING THE INTERSTITIAL FLUID COMPARTMENT OF THE BRAIN

Microanatomical evidence is presented that the intercellular fluid (IC F) compartment of the central nervous tissue is lined entirely and exc lusively by heavily glycosylated cells, with glycoconjugates exposed p rimarily at the apical cell surface, fronting the CSF or blood. On bot h common ependymal cells and on those specialised to form the choroid plexus epithelium, oligosaccharides coat the cilia and microvilli at t he apical surface, and also the smoother lateral and basal cell surfac es. In the ependyma, folded and wrinkled structures seem especially as sociated with freely exposed carbohydrates. On cerebral endothelial ce lls, oligosaccharides coat the luminal surface densely and the basal s urface lightly. The patterns of carbohydrate distribution thus vary fr om one cell type to another, but the different cell types all bear ess entially the same set of oligosaccharides, variations being due largel y to degree of terminal sialylation. Furthermore, the same set of olig osaccharides borders the brain in a broad spectrum of mammals, includi ng pouched and placental mammals. In both epithelia and endothelia, th e lectin binding sites visualised in fixed and embedded preparations w ere shown to be exposed likewise at the cell surfaces in unfixed tissu es and so able to bind molecules present in the fluid (CSF or blood) b athing the cells in vivo. This phylogenetically ancient enclosure of t he ICF compartment in a ''ring of sugars'' is suggested to relate to r egulation of the central neuronal microenvironment.