Developmental Exercise Effects on Adult Brain and Behavior

Among affluent populations, sedentary behavior is an increasing concern, particularly for children and adolescents who require daily exercise. Exercise results in a myriad of positive effects on brain and behavior, but whether these effects during development carry over into adulthood is largely unknown. Environmental enrichment research demonstrates the impact of early life experiences on adult brain and behavior, and emerging evidence on early life exercise follows a similar pattern, particularly for cognition. The hippocampus, which continues to develop in adolescence, is part of the stress circuitry and plays a role in emotion. Exercise conditions this circuitry without psychological stress. The hippocampus can also generate new neurons through quiescent (idling) stem cells in the dentate gyrus (DG), a pool of cells available to proliferate (eg. after a stimulus) and thus represent a form of structural plasticity. The present study examines the lasting effects of developmental exercise on adulthood brain and behavior. Specifically, it was hypothesized that adolescent exercise history would buffer chronic stress effects (and thus enhance stress resilience) in measures of affective behavior and structural plasticity in the DG in adulthood. Behavioral assessment of anxiety- and depressive-like behaviors demonstrated stress increased these behaviors and that exercise may promote partial stress resilience in males. Females demonstrated little to no behavioral changes in affect due to stress or exercise. There were also no long-term effects of exercise on quiescent stem cell populations in the DG, nor any protective effect from stress in the number of proliferating, quiescent stem cells. Proliferating stem cells were reduced by stress in males. However, exercise increased brain size in adulthood. Given that the results suggest that developmental exercise promotes stress resilience in depressive-like behavior in males, further research on coping strategies may elucidate how exercise promotes specific stress resilient behaviors in adulthood. The lack of structural plasticity effects but increase in brain size point towards examining other brain structural elements, such as glial cells. The lack of overall effects on females suggest that further research is necessary to understand how female brain and behavior is altered by chronic stress prior to examining carry-over effects of developmental exercise.