Inducible nitric oxide synthase expression in cultures enriched for matureoligodendrocytes is due to microglia

Expression of inducible nitric oxide (NO) synthase (NOS-2) occurs during in flammation in the central nervous system (CNS) and has been linked to demye lination accompanying certain CNS inflammatory diseases. Although astrocyte s and microglia are thought to be the major sources of NOS-2 expression in the CNS in vivo, recent evidence suggested that the myelin-producing oligod endrocytes (OLs) themselves can express NOS-2 in culture. Given the potenti ally important pathological implications of this finding, the purpose of th is study was to examine further the expression of NOS-2 by OLs in vitro. Af ter exposure to lipopolysaccharide (LPS) and interferon-gamma (IFN gamma), primary cultures enriched for mature OLs released NO in a time-dependent ma nner, although the amount varied considerably between different culture pre parations, Increased NO production was accompanied by expression of NOS-2 m RNA and protein, as determined by reverse transcriptase-polymerase chain re action (RT-PCR) and Western blot analysis, respectively. Immunoflourescence analysis revealed that the cell-type expressing NOS-2 in these cultures wa s galactocerebroside (Gal C)-negative but CD11b-positive. Further, NO produ ction could be attenuated in cultures treated with the microglial/macrophag e toxin, leucine methyl ester, prior to LPS/IFN gamma stimulation. Thus, mi croglia were the source of NOS-2 catalytic activity in these cultures, The present results indicate that LPS and IFN gamma are not effective stimuli f or induction of NOS-2 in OLs in primary cell culture. J, Neurosci, Res. 56: 189-198, 1999, (C) 1999 Wiley-Liss, Inc.