Abstract

Exercise increases the expression of brain-derived neurotrophic factor (BDNF) in the brain and contributes to cognitive and sensorimotor functions. This study aimed to elucidate how repeated exercise modifies BDNF expression elicited by a single bout of exercise in the brain using in vivo bioluminescence imaging (BLI). Bdnf-luciferase (Luc) mice with the firefly luciferase gene inserted at the translation start point of the Bdnf gene were used for BLI to monitor changes in BDNF expression in the brain. The treadmill exercise at a speed of 10 m/s for 60 min was repeated 5 days a week for 4 weeks. BLI in individual subjects was repeated four times: before the exercise intervention, on the first exercise day, and 14 and 28 days after the start of the intervention. Each BLI was performed after a single bout of exercise and monitored for 8 h after exercise. Repetitive BLI showed that the exercise regimen enhanced BDNF expression in the brain, specifically at 4-8 h after a single bout of exercise. Repeated exercise for 2 weeks accelerated the start of enhancement after a single bout of exercise, but not after 4 weeks of repeated exercise. This study showed that repeated exercise modulated the time window of exercise-enhanced BDNF expression, suggesting that repeated exercise could change the sensitivity of gene expression to a single bout of exercise. These findings can be attributed to the advantages of in vivo BLI, which allowed us to precisely measure the time course of BDNF expression after repeated exercise in individual subjects.