Exercise and brain neurotransmission.

Physical exercise influences the central dopaminergic, noradrenergic and serotonergic systems. A number of studies have examined brain noradrenaline (norepinephrine), serotonin (5-hydroxytryptamine; 5-HT) and dopamine with exercise. Although there are great discrepancies in experimental protocols, the results indicate that there is evidence in favour of changes in synthesis and metabolism of monoamines during exercise. There is a possibility that the interactions between brain neurotransmitters and their specific receptors could play a role in the onset of fatigue during prolonged exercise. The data on the effects of branched chain amino acid (BCAA) supplementation and 'central fatigue' seem to be conflicting, although recent studies suggest that BCAA supplementation has no influence on endurance performance. There are numerous levels at which central neurotransmitters can affect motor behaviour; from sensory perception, and sensory-motor integration, to motor effector mechanisms. However, the crucial point is whether or not the changes in neurotransmitter levels trigger or reflect changes in monoamine release. Until recently most studies were done on homogenised tissue, which gives no indication of the dynamic release of neurotransmitters in the extracellular space of living organisms. Recently, new techniques such as microdialysis are voltammetry were introduced to measure in vivo release of neurotransmitters. Microdialysis can collect virtually any substance from the brain of a freely moving animal with a limited amount of tissue trauma. This method allows measurement of local neurotransmitter release during on-going behavioural changes such as exercise. The results of the first studies using these methods indicate that the release of most neurotransmitters is influenced by exercise. Although the few studies that have been published to date show some discrepancies, we feel that these recently developed and more sophisticated in vivo methods will improve our insight into the relationship between the monoamine and other transmitters during exercise. Continued quantitative and qualitative research needs to be conducted so that a further understanding of the effects of exercise on brain neurotransmission can be gained.