ULTRASTRUCTURAL AND IMMUNOHISTOCHEMICAL CHANGES OF FLUORESCENT GRANULAR PERITHELIAL CELLS AND THE INTERACTION OF FGP CELLS TO MICROGLIA AFTER LIPOPOLYSACCHARIDE ADMINISTRATION

Fluorescent granular perithelial (FGP) cells introduced by Mate et al. (1979, 1980, 1981) are situated in the Virchow-Robin space of cerebra l microvessels and exhibit a marked uptake capacity for the endo- and exogenous materials in physiological conditions. That is, the FGP cell s are the perivascular macrophage lineage enclosed by a basal lamina a nd glia limitans and are distributed between blood vessels and cerebra l parenchyma. As reported previously, the FGP cells were distinguishab le from microglia and pericytes in their morphology, location, and epi topes on their cytoplasmic membrane. On the other hand, it is establis hed that microglia are upregulated by lipopolysaccaride (LPS) administ ration, but it remains unsettled whether the FGP cells, the perivascul ar macrophagic cells, are activated by LPS or not and what role the FG P cells play in the upregulation of microglia. Thus far, the morpholog ical relationship between FGP cells and microglia in the process of up regulation has not been clarified.Thirty-six 7-month-old Wistar male r ats were employed. The animals were sacrificed at 2, 5, 10, 24, and 72 h after the intravenous administration of 500 mu g/kg of LPS. The FGP cells and microglia in their cerebral cortex were studied with immuno histochemical and electron microscopical techniques. The findings of t he present study indicated that the majority of FGP cells were upregul ated by LPS from the results of immunohistochemical and morphological data, but some of them tended to degenerate. Furthermore, in the time course after LPS administration, microglia were also upregulated and a pproached the microvessels and occasionally contacted the FGP cells di rectly. From these findings, it is hypothesized that FGP cells may sig nificantly influence the mobilization and upregulation of microglia ca used by LPS administration. Anat. Rec. 251:330-338, 1998. (C) 1998 Wil ey-Liss, Inc.