Immuno-electron microscopic study of the distribution of the S 100 protein in brain glial cells.

The distribution of the brain-specific S 100 protein was studied by an immunohistochemical method at the ultrastructural level. The S 100 protein was localized in the plasma membrane of astrocytes, oligodendrocytes and neurons, but not in that of endothelial cells and pericytes. Astrocytic filaments also possessed S 100 activity. The vascular basement membrane lacked traces of S 100.