Efeito do treinamento físico sobre a modulação do sistema dopaminérgico central

Abstract

This study aimed to verify if the adaptations resulting from aerobic physical training are related to the modulation of central monoamines, mainly of the dopaminergic system, in the caudate putamen (CPU) in the preoptic area (APO), and the amygdala (Amy). These regions are involved in motor and body temperature control and the reward system, being important for performance during exercise. For this, Wistar rats aged 3-4 weeks were used, divided into: untrained (NT, n=38) and trained (T, n=41) groups. Physical training was performed on a treadmill for 8 weeks/5 days a week, reaching a speed of 18 m.min-1 and a duration of 60 minutes. After training, the groups were divided into two protocols. In the first, the animals remained resting on the treadmill for 60 minutes or performed constant exercise (70% of maximum speed) for 30 minutes or until fatigue. In the three experimental situations, oxygen consumption, respiratory quotient and body temperature were recorded. During exercise, work and energy expenditure were calculated. Immediately after the experiment, the animals were euthanized and the brain was removed for monoamine dosage in the areas of interest. In the second protocol, the animals NT and T were euthanized 48 hours after the last physical exercise session, and the brain was removed to quantify the protein expression of the DRD2 receptor. The results showed that in the CPU, physical training increased the dopaminergic turnover by 35% at rest as well as by 55% at the time of fatigue. Furthermore, in the CPU, physical training increased the serotonergic turnover at fatigue by 65% and reduced the noradrenergic content by 22% during the steady-state phase of constant exercise. At Amy, exercise training increased dopaminergic turnover by 46% at rest as well as 43% at the time of fatigue. In both nuclei, the greater dopaminergic activity was related to the greater work performed until fatigue by the T animals, as well as with the lower respiratory quotient of these animals, indicating the participation of the dopaminergic system in the improvement of performance and the use of energetic substrates after the physical training. During the stable phase of the exercise, dopaminergic turnover in Amy showed a 29% reduction in T animals. Such a decrease in dopaminergic activity was related to the lower energy expenditure of these animals during the stable phase of exercise. Associated with modulation of dopaminergic turnover in Amy, T animals showed a 52% increase in protein expression of DRD2 receptors. Although the serotonergic system was not modified in Amy, the 5-HT/DA ratio in this area was 43% lower in T animals during the stable phase of the exercise, and this reduction was related to the lower respiratory quotient of T animals. For APO, no changes were observed in catecholamines induced by physical training. Based on the results achieved, it is concluded that the ergogenic effect of aerobic physical training is related to greater basal dopaminergic activity and fatigue in brain areas related to motor control and to motivation and reward.