BDNF and major depressive disorder: SCNA (which encodes alpha-synuclein) regulates monoamine neurotransmitters and inhibits BDNF/TrkB signaling50 (which is altered by early life and adult stress in mesocorticolimbic regions and associated with depression-like behavior51,52), and is also dysregulated in serum of depressed patients53 and hippocampus of rats after stress across the lifespan54,55.