Abstract
Life experiences at early ages, such as physical activity in childhood and adolescence, can result in long-lasting brain effects able to reduce future risk of brain disorders and to enhance lifelong brain functions. However, how early physical exercise promotes these effects remains unclear. A possible hypothesis is that physical exercise increases the expression of neurotrophic factors and stimulates neuronal growth, resulting in a neural reserve to be used at later ages. Basing our study on this hypothesis, we evaluated the absolute number and morphology of neuronal cells, as well as the expression of growth, proliferation and survival proteins (BDNF, Akt, mTOR, p70S6K, ERK and CREB) in the cerebral cortex and hippocampal formation throughout of a sedentary period of rats who were physically active during youth. To do this, male Wistar rats were submitted to an aerobic exercise protocol from the 21st to the 60th postnatal days (P21–P60), and evaluated at 0 (P60), 30 (P90) and 60 (P120) days after the last exercise session. Results showed that juvenile exercise increased, and maintained elevated, the number of cortical and hippocampal neuronal cells and dendritic arborization, when evaluated at the above post-exercise ages. Hippocampal BDNF levels and cortical mTOR expression were found to be increased at P60, but were restored to control levels at P90 and P120. Overall, these findings indicate that, despite the short-term effects on growth and survival proteins, early exercise induces long-lasting morphological changes in cortical and hippocampal neurons even during a sedentary period of rats.
Highlights
Life experiences at early ages, such as physical activity in childhood and adolescence, can result in longlasting brain effects able to reduce future risk of brain disorders and to enhance lifelong brain functions
In the hippocampal formation, the number of non-neuronal cells was found to be increased at P120 in rats from the EX group (p < 0.05), but not in those from the CTL group (p > 0.05) (Fig. 1)
When comparing studied groups (EX vs CTL), post-hoc analysis showed that early exercise increased the cortical number of neuronal and non-neuronal cells at P60, particularly when comparing ages 90 (P90) and P120 (p < 0.05)
Summary
Life experiences at early ages, such as physical activity in childhood and adolescence, can result in longlasting brain effects able to reduce future risk of brain disorders and to enhance lifelong brain functions. Hippocampal BDNF levels and cortical mTOR expression were found to be increased at P60, but were restored to control levels at P90 and P120 Overall, these findings indicate that, despite the short-term effects on growth and survival proteins, early exercise induces long-lasting morphological changes in cortical and hippocampal neurons even during a sedentary period of rats. Another important finding is that early physical activity improves the ability to evoke spatial memories in later life[7] This finding supports previous research in humans that has shown a correlation between physical activity at an early age and long-lasting benefits on brain functions[2]. Even though these findings are promising, the stability or permanence of brain changes which result from early exercise after it has been interrupted are still unclear
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