Recent studies demonstrate that BDNF[32,33], neurotrophin-3 (NT-3)[34], glial cell line-derived neurotrophic factor (GDNF)[35], fibroblast growth factor-2 (FGF-2)[36] and nerve growth factor (NGF)[37] influence adult hippocampal neurogenesis and regulate synaptic plasticity in neuronal networks involved in major depression. This evidence concerns the gene GDNF and major depressive disorder.