Changes in the bovine zona pellucida induced by plasmin or embryonic plasminogen activator

Fluorescent granular perithelial (FGP) cells introduced by Mato et al. (1979, 1980, 1981) are situated in the Virchow-Robin space of cerebral microvessels and exhibit a marked uptake capacity for the endo- and exogenous materials in physiological conditions. That is, the FGP cells are the perivascular macrophage lineage enclosed by a basal lamina and glia limitans and are distributed between blood vessels and cerebral parenchyma. As reported previously, the FGP cells were distinguishable from microglia and pericytes in their morphology, location, and epitopes on their cytoplasmic membrane. On the other hand, it is established that microglia are upregulated by lipopolysaccaride (LPS) administration, but it remains unsettled whether the FGP cells, the perivascular macrophagic cells, are activated by LPS or not and what role the FGP cells play in the upregulation of microglia. Thus far, the morphological relationship between FGP cells and microglia in the process of upregulation has not been clarified. Thirty-six 7-month-old Wistar male rats were employed. The animals were sacrificed at 2, 5, 10, 24, and 72 h after the intravenous administration of 500 microg/kg of LPS. The FGP cells and microglia in their cerebral cortex were studied with immunohistochemical and electron microscopical techniques. The findings of the present study indicated that the majority of FGP cells were upregulated 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 approached the microvessels and occasionally contacted the FGP cells directly. From these findings, it is hypothesized that FGP cells may significantly influence the mobilization and upregulation of microglia caused by LPS administration.