Effects of acute physical exercise on central serotonergic systems

This paper reviews data concerning the effects of acute physical exercise
(treadmill running) in trained rats. Works from the 1980’s have established that
acute running increases brain serotonin (5-hydroxytryptamine: 5-HT) synthesis in
two ways. Lipolysis-elicited release of free fatty acids in the blood compartment
displaces the binding of the essential amino acid tryptophan to albumin, thereby
increasing the concentration of the so-called “free tryptophan” portion, and
because exercise increases the ratio of circulating free tryptophan to the sum of
the concentrations of the amino acids that compete with tryptophan for uptake at
the blood-brain barrier level, tryptophan enters markedly in the brain
compartment. However, this marked increase in central tryptophan levels increases
only to a low extent brain 5-HT synthesis, as assessed by the analysis of
5-hydroxyindoleacetic acid levels, thereby suggesting that exercise promotes
feedback regulatory mechanisms. Indirect indices of 5-HT functions open the
possibility that acute exercise-induced increases in 5-HT biosynthesis are
associated with (or lead to) increases in 5-HT release. Lastly, the hypothesis
that training and/or acute exercise triggers changes in 5-HT receptors has been
examined in several studies; actually, both positive and negative results have
been reached. Taken together, all these data support the need for future studies
on the functional effects of exercise on 5-HT, including those related to the
hypothesis that the positive mood effects of exercise rely (partly or totally) on
central serotonergic systems.

 

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