BDNF and major depressive disorder: Voluntary exercise has been found to mitigate harmful consequences of stress on the brain and to prevent the expression of depression and anxiety-like behavior [1].Increased activity of brain-derived neurotrophic factor (BDNF) signaling is suggested to be an important factor mediating the benefits seen after running.In agreement, stress and depression have been found to decrease BDNF expression [2, 3].