Effects of inactivity and exercise intervention on brain-derived neurotrophic factor in mice: Comparison of kinetics in serum, skeletal muscle, and brain.

Exercise training increases brain-derived neurotrophic factor (BDNF) expression and improves cognitive function. However, the dynamics of BDNF during inactivity and the effects of exercise intervention on BDNF levels have rarely been examined. Therefore, we aimed to examine changes in serum, skeletal muscle, and brain BDNF levels under these conditions. Mice were divided into control (Co), cast immobilization (CI), reloading (RL), and exercise (Ex) groups. Muscle atrophy was induced by cast immobilization for 2 weeks in the CI, RL, and Ex groups. After cast removal, the RL and Ex groups underwent regrounding and treadmill exercise, respectively, for 2 weeks. Serum, skeletal muscle, and brain BDNF levels showed a similar decreasing trend in the CI group, recovery in the RL group, and a further increase in the Ex group compared with those in the Co group. This indicates that BDNF levels change in parallel with the degree of activity. However, the magnitude of variation differed among the tissues in the order of serum > skeletal muscle > brain tissue. These results suggest that different mechanisms in different tissues regulate BDNF expression. BDNF could potentially act as an objective measure of the impact of both inactivity and exercise-based interventions.