Other authors studied the association between cytokines and depression in an animal model and found that rats exposed to chronic mild stress for four weeks showed depression-like behavioral changes and altered expression of cytokines in the brain, with elevated levels of proinflammatory cytokines (IL-1β, TNF-α, and IL-6) and decreased levels of TGF-β and IL-10 [74]. This evidence concerns the gene IL1B and major depressive disorder.