GDNF and depressive disorder: Acute or chronic administration of antidepressants increasing the levels of synaptic serotonin (such as tricyclic antidepressants, tetracyclic antidepressants, and serotonin-selective reuptake inhibitors) is indeed able to increase GDNF expression both in cell culture (Mercier et al., 2004; Hisaoka et al., 2007; Golan et al., 2011; Kajitani et al., 2012; Hisaoka-Nakashima et al., 2015; 2019; Abe et al., 2019) and in serum of patients with depression (Zhang et al., 2008).