NOS2 and major depressive disorder: In rat models of depression, the levels of the oxidative stress indicators including inducible nitric oxide synthase (iNOS) and malondialdehyde (MDA) in the hippocampal region significantly increased, and the levels of superoxide dismutase (SOD) and glutathione (GSH) decreased,15 indicating that depressive behaviour is significantly related to oxidative stress damage in the hippocampal region.