A stress-triggered depressive phenotype also shows altered levels of BDNF protein.93 Furthermore, chronic stress impairs synaptic transmission, leading to downregulation of BDNF and resulting in sustained oxidative stress; this ultimately leads to a depression-like phenotype,94,95 and learning and memory deficits.5,96 This can be prevented by antioxidant treatment.19H. This evidence concerns the gene BDNF and major depressive disorder.