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Neurotrophic factors 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 P 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. 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.
These words have special meaning because they reflect the importance of life experiences. In this context, it has been reported that early life experiences, such as physical activity in childhood and adolescence, can induce long-lasting brain effects 1 , 2 , 3. For instance, a prospective population-based study showed a positive relationship between physical activity at 15 and 25 years of age and information processing speed at 62 and 85 years of age 2.
In another study, physical fitness at age 18 predicted occupational status and educational achievement later in life 1. It has been also observed that older women who were physically active during their adolescence showed better cognitive performance and had a lower likelihood of cognitive impairment in late life compared with those who were physically inactive 3. However, how early physical activity promotes these effects remains unclear. Studies on rodents have shown that early exercise increases axonal and neuronal density and enhances brain-derived neurotrophic factor BDNF expression and its receptor tropomyosin-related kinase B TrkB in the hippocampal formation 6 , 7 , a brain structure which is related to mnemonic and emotional processes.