Fatigue (the inability to maintain power output) during prolonged exercise has traditionally been attributed to inhibition of skeletal muscle contractile mechanisms. Recently, it has been hypothesized that fatigue during endurance exercise may be influenced by activity of the brain serotonergic system (Newsholme et al. 1987). More specifically, Newsholme et al. (1987) postulated that increasing levels of brain serotonin (5-HT) may result in feelings of lethargy and loss of drive which ultimately result in a reduction in power output and fatigue. During prolonged exercise, increasing levels of plasma free fatty acids displace tryptophan (TRP; 5-HT's precursor) from albumin (Newsholme & Leech 1983). Unbound TRP is then transported into the brain and 5-HT synthesis in increased (Chaouloff et al. 1987, Blomstrand et al. 1989). A recent investigation indicated that increased levels of free-TRP in the blood of humans, subsequent to exercise, results in impaired mental performance (Blomstrand et al. 1991). However, the relationship between brain 5-HT activity and physical performance has yet to be established. Increased brain 5-HT activity could also impair endurance performance through its negative effects on brain dopamine (DA) synthesis (Spampinato et al. 1985). The purpose of this investigation was to examine the effects of increased 5-HT activity on endurance performance and brain dopamine turnover in the rat.
Acta Physiol Scand. 145(1):75-76.