BACKGROUND:Cerebral white matter demyelination is outstanding in the images of delayed encephalopathy after acute carbon monoxide (CO) poisoning. Since Nogo-A and Nogo-receptor are expressed in onoligodendrocytes and neurons respectively, we infer that Nogo-A system is involved in brain injury after acute CO poisoning and related to delayed encephalopathy after acute CO poisoning. Endogenous CO is a gaseous messenger, which is the metabolic product of hemeoxygenase. There is no report about the CO effect on Nogo-A system til now. OBIECTIVE: To in vitro culture oligodendrocytes using endogenous CO, inhibit the activity of hemeoxygenase system using zinc protoporphyrin-IX (ZnPPIX) and observe the variation of Nogo-A in oligodendrocytes at mRNA and protein levels. METHODS: Rat oligodendrocytes cultured in vitro were divided into control, CO, ZnPPIX groups. Cels in the CO and ZnPPIX groups were treated with 1% CO directly, In the ZnPPIX group, 10 μmol/L ZnPPIX was added into the culture medium before CO treatment. The expressions of Nogo-A mRNA and protein at 6, 24, 48 hours after culture were compared. Differences in the peak levels of Nogo-A mRNA and protein between CO and ZnPPIX groups were detected using RT-PCR and immunohistochemistry respectively. RESULTS: The expression levels of Nogo-A mRNA and protein were significantly higher in the CO group than the control group and reached the peak at 24 hours of culture. Compared with the CO group, oligodendrocytes cultured with ZnPPIX showed higher expressions of Nogo-A mRNA and protein at 24 hours of culture. These findings suggest that except the influence of hypoxia occurring in CO poisoning, exogenous CO increases the expression of Nogo-A in cultured oligodendrocytes in vitro, and the heme oxygenase system can inhibit the expression of Nogo-A mRNA and protein.