PERIVASCULAR CELLS ACT AS SCAVENGERS IN THE CEREBRAL PERIVASCULAR SPACES AND REMAIN DISTINCT FROM PERICYTES, MICROGLIA AND MACROPHAGES

Perivascular cells in the rat brain are an immunophenotypically define d group of cells which can be identified by their expression of the ED 2 antigen.The present study investigates the role of perivascular cell s as scavengers in the perivascular spaces of the rat brain and the re lationship of these cells to microglia, macrophages, pericytes and smo oth muscle cells. Particulate matter (Indian ink) was injected selecti vely into the perivascular spaces of the left caudoputamen of 59 rats. Animals were killed by cardiac perfusion of formalin or glutaraldehyd e 2 h-2 years after ink injection. Cerebral hemispheres were examined histologically and immunocytochemically using the ED2 antibody for per ivascular cells, ED1 for microglia and macrophages and OX-6 directed a gainst la antigen [major histocompatibility complex (MHC) class II]. E D2+ perivascular cells ingested Indian ink in the perivascular spaces and expressed MHC class II antigen. Reactive microglia and macrophages in the perivascular parenchyma expressed ED1, but no ED2+ cells were seen outside the perivascular spaces. Transmission electron microscopy distinguished perivascular cells, which ingested carbon particles, fr om pericytes. which did not. The results of this study suggest that pe rivascular cells remain distinct from pericytes, microglia and macroph ages and that they play a major role as scavengers in the perivascular spaces of the rat brain. This role reflects the importance of perivas cular spaces as drainage pathways for soluble and insoluble material f rom the brain.