Involvement of specific macrophage-lineage cells surrounding arterioles in barrier and scavenger function in brain cortex.

The transport of solutes between blood and brain is regulated by a specific barrier. Capillary endothelial cells of brain are known to mediate barrier function and facilitate transport. Here we report that specific cells surrounding arterioles, known as Mato's fluorescent granular perithelial (FGP) cells or perivascular microglial cells, contribute to the barrier function. Immunohistochemical and in situ hybridization studies indicate that, in normal brain cortex, type I and type II macrophage scavenger receptors are expressed only in FGP/perivascular microglial cells, and surface markers of macrophage lineage are also detected on them. These cells mediate the uptake of macromolecules, including modified low density lipoprotein, horseradish peroxidase, and ferritin injected either into the blood or into the cerebral ventricles. Accumulation of scavenged materials with aging or after the administration of a high-fat diet results in the formation of honeycomb-like foam cells and the narrowing of the lumen of arterioles in the brain cortex. These results indicate involvement of FGP/perivascular microglial cells in the barrier and scavenger functions in the central nervous system.

Study on distribution of pericyte and fluorescent granular perithelial (FGP) cell in the transitional region between arteriole and capillary in rat cerebral cortex.

BACKGROUND: The FGP (fluorescent granular perithelial) cell nominated by M. Mato were distributed around small cerebral vessels and potent in the uptake capacity. They are provided with surface antigens related to macrophage lineage. The aim of this report is to show the regional distribution of pericytes and novel perivascular cells (FGP cell) in relation to the glia limitans and basal lamina. METHODS: The perietal cortex of rat cerebrum were fixed with a mixture containing 2.5% glutaraldehyde and 2% paraformaldehyde with or without 1% tannic acid and 1% osmium tetroxide buffered with 0.1 M phosphate. The specimens were embedded in Epon 812 and cut serially and observed with the light microscope. After selecting the appropriate region of blood vessels in the sections, they were reembedded in Epon 812 and were prepared for electron microscopic observation. RESULTS: Fixatives containing tannic acid gave good results for the discrimination between the glia limitans and the basal lamina at an electron microscopical level. The FGP cells were situated in the interstices between thick basal lamina of blood vessel and thin glia limitans of astrocyte (Virchow Robin space). In the terminal part of cerebral arteriole, the vascular basal lamina abutted against the glia limitans and both laminae were fused. The basal lamina enclosing pericytes was common to endothelium and the basal lamina of capillary was assumed to be the composite of proper basal lamina and glia limitans. Subsequently, the FGP cells surround only arteriole and venule, whereas the pericytes belong to capillaries. At the boundary of arterioles and capillaries, FGP cells coexisted with pericytes and were localized at the external site of pericytes bordering with basal lamina. CONCLUSIONS: Based on these findings, the FGP cells were different from pericytes in their localization and distribution. Some roles of FGP cells in cerebral metabolism are discussed.