Immunocytochemical basis for a meningeo-glial network

Abstract

Evidence is presented here for a cellular network that courses through all layers of meninges, the vasculature of both the brain and meninges, and extends into the brain parenchyma. Confocal mapping of calcium-binding protein S100beta immunoreactivity (S100beta-ir) and of the intermediate filament vimentin-ir through serial sections of the meningeal-intact adult rat brain revealed this network. In all tissues examined, S100beta-ir and vimentin-ir were primarily colocalized, and were found in cells with elongated processes through which these cells contacted one another to form a network. The location of labeling and the morphology of the cells labeled were consistent with the possibility that this network consists of fibroblasts in the meninges and the walls of large blood vessels, of pericytes at the level of capillaries, and of ependymocytes and a population of astrocytes in the brain parenchyma. At many sites along the borders of the brain parenchyma itself and of the brain blood vessels, it was possible to detect S100beta-ir and vimentin-ir cell processes that cross the basal laminae. This suggested the probable means by which the S100beta-ir cells of the extraparenchymal tissues anatomically contact the cells that express the same markers in the brain. Privileged anatomical relationships of the S100beta/vimentin network with the glial fibrillary acidic protein (GFAP) astrocytes further suggested that, together, they form the structural basis for a general meningeo-glial network. This organization challenges the current model of brain architecture, calls for a reconsideration of the role of meninges and vascular tissues, and appears to reflect the existence of hitherto unsuspected systems of communication.