IDO1 and major depressive disorder: In the present study, we established a mouse depression model by peripheral administration of LPS, and measured the concentration of the pro-inflammatory cytokines, TNF-α, IL-1β, and interferon γ (IFN-γ), in peripheral blood, the concentration of IFN-γ in the brain, the expression of NF-κB P65 and IDO in the hippocampus, and the concentration of calcium in the brain.