-mediated oligodendrocyte death is a direct effect and not mediated through microglia or by nitric oxide
(A) Number of viable oligodendrocytes in cocultures of oligodendrocytes and ameboid microglia treated with IFNγ or PBS for 48 hr. Oligodendrocytes and microglia were plated together each at a density of 10,000 cells/mm2 on glass coverslips. Cocultures were treated with IFNγ or PBS. (B) NADPH diaphorase staining of rat ameboid microglia exposed to PBS (control), IFNγ, or LPS for 24 hr. NADPH diaphorase positive microglia stain intensly purple-black. (C) Number of viable oligodendrocytes 48 hr after coculture 1 mm beneath microglia containing inserts pretreated with IFNγ or PBS. Ameboid microglia were cultured on membranes with 1.6 × 106 pores/cm2, and an average pore size of 0.45 µm. After treatment with IFNγ or PBS for 24 hr, inserts were washed with five 30-min incubations in fresh culture medium. Washed inserts were then placed over coverslips of oligodendrocytes in the presence of PBS, anti-IFNγ antibodies, hemoglobin (Hg) or Nω-methyl-L-arginine (NMA). (D) Number of viable oligodendrocytes 48 hr after coculture 1 mm beneath primary rat fibroblast containing inserts under conditions described above for Panel C.