TGFB1 and major depressive disorder: Likewise, a decrease of TGF-β1 levels has been observed in hippocampus and cortex of animal models of depression (Yu et al., 2011); furthermore, several studies carried out in depressed patients have demonstrated that plasma TGF-β1 levels are reduced and correlate with depression severity (Myint et al., 2005; Rush et al., 2016).