"bdnf appears to play a role in both neurobiology and metabolism. studies have demonstrated that physical exercise may increase circulating bdnf levels in humans. to identify whether the brain is a source of bdnf during exercise, eight volunteers rowed for 4 h while simultaneous blood samples were obtained from the radial artery and the internal jugular vein. to further identify the putative cerebral region(s) responsible for bdnf release, mouse brains were dissected and analysed for bdnf mrna expression following treadmill exercise. in humans, a bdnf release from the brain was observed at rest and increased 2- to 3-fold during exercise. both at rest and during exercise, the brain contributed 70–80% of the circulating bdnf, while this contribution decreased following 1 h of recovery. in mice, exercise induced a 3- to 5-fold increase in bdnf mrna expression in the hippocampus and cortex, peaking 2 h after the termination of exercise. these results suggest that the brain is a major but not the sole contributor to circulating bdnf. moreover, the importance of the cortex and hippocampus as sources of plasma bdnf becomes even more prominent in the response to exercise.”