| Neuroplasticity is defined as a change in neural system performance based on experience. Neuroplasticity is important throughout life in order to respond to ever-changing conditions or insults such as ageing or disease. One intervention thought to aid in maintaining neural plasticity and health is physical exercise. Exercise is correlated with increased neuronal survival, neurogenesis and learning. However, the mechanisms behind these alterations are not completely understood. One class of neurochemicals with the necessary characteristics to mediate exercise-induced neuroplasticity is the neurotrophins. Neurotrophins promote the survival of neurons, enhance synaptic transmission and reciprocally affect other neurochemicals involved in plasticity such as serotonin. Initial investigations suggested that serotonin is involved in long-term modulation of the exercise ventilatory response following repeated bouts of hypercapnic exercise, a form of exercise-induced neuroplasticity. Since neurotrophins are influenced by and in turn affect serotonin levels, we analyzed brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) in the ventral spinal cord of rats following repeated bouts of normocapnic or hypercapnic exercise. However, our results provided no evidence that ventral spinal BDNF and NT-3 play a major role in the mechanisms underlying exercise-induced neuroplasticity. We then focused our investigations on the hippocampus, an area involved in long-term potentiation (a physiological model of neuroplasticity thought to underlie memory storage and retrieval). We found that following exercise, hippocampal BDNF levels increase and are positively correlated to distance run, effects that are enhanced in mice genetically selected for increased wheel running. In addition, levels of hippocampal BDNF are affected by rat strain, indicating possible genetic influences in hippocampal BDNF expression and regulation. Our investigations may give insight into mechanisms controlling neuroplasticity. For example, the enhancement of neurotrophin levels by exercise may lead to a greater capacity for the neural system to adapt to changing environmental or physiological conditions. |
