Brain-derived neurotrophic factor (BDNF) promotes the survival and growth of neurons. Levels of BDNF are increased through stimuli like exercise. Two studies in rats found that physical activity and antidepressant treatment have an additive effect in increasing hippocampal BDNF levels. A second study found that direct infusion of BDNF into the hippocampus of rats produced antidepressant effects, suggesting BDNF promotes the effects of antidepressants. Increased BDNF through exercise may help increase neural plasticity and protect against neural degeneration, as well as help reduce depression by positively impacting mood.