Previous research had linked physical exertion with higher levels of neuronal growth factors known as neurotrophins in the spinal cord and skeletal muscles. In the new work, a team of researchers led by Raffaella Molteni at the University of California at Los Angeles and Jun-Qi Zheng of the A. I. DuPont Hospital for Children in Wilmington, Del., tested whether these exercise-related changes affect the brains ability to form new connections. The scientists gave rats access to a running wheel for periods ranging from zero to seven days. When they tested cultured cells taken from the animals, they found that those from the runners grew longer extensions known as neurites and that there was a direct correlation between how far the rats ran and how long the neurites became.
The team also tested whether exercise promoted regeneration in vivo. After damaging the nerves of rats, the researchers determined that significantly more axons recovered in those rats that had exercised for seven days prior to injury than in the sedentary animals. The authors further note that injecting a compound that inhibits neurotrophin receptors stopped the axon growth in the running rats, which suggests that neurotrophin signaling is responsible for the regenerative effect.