Exercise Induces Age-Dependent Neuroplastic Changes in Brain Regions Responsible for Learning Memory and Emotional Behavior

During early-life, the brain experiences a variety of developmental adaptions and undergoes a period of immense neural pruning, making the brain more plastic and susceptible to change from external events. Exercise is one such event that produces a milieu of adaptive changes including improved brain plasticity and function, increases in hippocampal brain derived neurotrophic factor (BDNF), and BDNF-mediated enhancements in hippocampal function. Recent work has shown that exercise during early life has can produce long-lasting improvements in brain function that would normally be transient in adulthood. The specific developmental period during which the hippocampus is prone to exercise-induced neuroplastic changes, however, is unknown because previous studies testing the impacts of early life exercise had rats run across multiple developmental stages. The purpose of this study was to determine the impact that exercise has on BDNF if initiated during two different and clearly defined early life developmental periods, the early juvenile period immediately post weaning versus the pubescent period surrounding puberty onset. Hippocampal BDNF mRNA levels were measured following one week of exercise and after 14 days following exercise cessation in juvenile (approx. postnatal day 24), pubescent (approx. postnatal day 40), and in adult rats (approx. postnatal day 7). Exercise produced significant increases in BDNF mRNA compared to sedentary matched counterparts across all ages in the dentate gyrus immediately following one week of exercise. Juvenile rats exhibited a trend towards long-lasting increases in BDNF 14 days after exercise within the dentate gyrus and the CA3. Thus, exercise produced trends toward enduring increases in BDNF when initiated before puberty. These data suggest that the juvenile brain may have the greatest propensity for long term increases in BDNF following exercise.