IDO1 and major depressive disorder: Zhou and his team studied an animal model of neuropathic pain, namely spared nerve injury (SNI) induced in mice and followed the rates of indoleamine 2,3-dioxydase-1 (IDO1) enzyme, which metabolizes tryptophan involved in the inflammatory process, cerebral inflammation being a demonstrated process with a role in depression [47] as compared to sham mice (n = 6–20 in each group).