A postmortem study on characters with MDD found that the level of GDNF decreased in PFC and the concentration of GDNF in the amygdala reduced as well (Michel et al., 2008; Järvelä et al., 2011; Tang et al., 2023), implying that lower serum GDNF may be involved in the pathophysiology of MDD. Here, GDNF is linked to major depressive disorder.