Exercise-induced changes in brain glucose and serotonin revealed by microdialysis in rat hippocampus: effect of glucose supplementation

The aim of this study was to assess extracellular glucose changes in hippoc ampus in response to physical exercise and to determine the influence of gl ucose supplementation. In the same time, we have observed the changes in se rotonin, in order to study the relationship between glucose and serotonin d uring exercise. Both glucose and serotonin were assessed using microdialysi s. Exercise induced an increase In extracellular glucose levels over baseli ne during exercise to 121.1 +/- 3.0% (P < 0.001), then a decrease to baseli ne during recovery. The serotonin followed glucose changes during the first 90 min of exercise, but followed a different pattern during recovery, incr easing to a maximum of 129.9 +/- 7.0% after 30 min of recovery (P < 0.001), When a 15% glucose solution was infused (10 muL min(-1)) during exercise a nd recovery, blood glucose concentration was increased, but extracellular b rain glucose decreased to reach a minimum of 73.3 +/- 4.6% after 90 min of recovery (P < 0.001). Serotonin was always the mirror-reflect of cerebral g lucose, with a maximum increase of 142.0 +/- 6.9% after 90 min of recovery (P < 0.001). These results show that exercise induces changes in brain gluc ose and 5-hydroxytryptamine (5-HT) levels, which were dramatically modified by glucose infusion. Taking into account the implication of brain 5-HT in central fatigue, they suggest that if glucose supplementation, before and d uring exercise, undoubtedly increase performance because of Its peripheral positive action, it would have a negative impact on the quality of recovery after the end of the exercise.