Immunocytochemical basis for a meningeo-glial network

Evidence is presented here for a cellular network that courses through all layers of meninges, the vasculature of both the brain and meninges, and ext ends into the brain parenchyma. Confocal mapping of calcium-binding protein S100 beta immunoreactivity (S100 beta-ir) and of the intermediate filament vimentin-ir through serial sections of the meningeal-intact adult rat brai n revealed this network. In all tissues examined, S100 beta-ir and vimentin -ir were primarily colocalized, and were found in cells with elongated proc esses through which these cells contacted one another to form a network. Th e location of labeling and the morphology of the cells labeled were consist ent with the possibility that this network consists of fibroblasts in the m eninges and the walls of large blood vessels, of pericytes at the level of capillaries, and of ependymocytes and a population of astrocytes in the bra in parenchyma. At many sites along the borders of the brain parenchyma itse lf and of the brain blood vessels, it was possible to detect S100 beta-ir a nd vimentin-ir cell processes that cross the basal laminae. This suggested the probable means by which the S100 beta-ir cells of the extraparenchymal tissues anatomically contact the cells that express the same markers in the brain. Privileged anatomical relationships of the S100 beta/vimentin netwo rk with the glial fibrillary acidic protein (GFAP) astrocytes further sugge sted that, together, they form the structural basis for a general meningeo- glial network. This organization challenges the current model of brain arch itecture, calls for a reconsideration of the role of meninges and vascular tissues, and appears to reflect the existence of hitherto unsuspected syste ms of communication. (C) 2000 Wiley-Liss, Inc.