Title

Enhanced availability of serotonin limits muscle activation during high-intensity, but not low-intensity, fatiguing contractions

Document Type

Journal Article

Publication Title

Journal of neurophysiology

Volume

128

Issue

4

First Page

751

Last Page

762

PubMed ID

36001790

Publisher

American Physiological Society

School

School of Medical and Health Sciences

Comments

Henderson, T. T., Taylor, J. L., Thorstensen, J. R., Tucker, M. G., & Kavanagh, J. J. (2022). Enhanced availability of serotonin limits muscle activation during high-intensity, but not low-intensity, fatiguing contractions. Journal of Neurophysiology, 128(4), 751-762.

https://doi.org/10.1152/jn.00182.2022

Abstract

Serotonin (5-HT) modulates motoneuron excitability during muscle contractions, where the release of 5-HT in the central nervous system (CNS) is linked to the intensity of physical activity. Although there is evidence that enhanced availability of 5-HT can exacerbate fatigue, these effects on the development of fatigue during different contraction intensities are largely unknown. The purpose of this study was to investigate how enhanced 5-HT availability affects voluntary muscle activation and corticospinal excitability during fatigue-inducing contractions. Two experiments were performed. In the first experiment (n = 11), 12 isometric elbow flexions at 20 % maximal voluntary contractions (MVCs) were performed for 2 min each with 40-s rest periods. In the second experiment (n = 14), 12 maximal isometric elbow flexions were held for 10 s each with 40-s rest periods. In both experiments, the selective serotonin reuptake inhibitor (20-mg paroxetine), or a placebo, was administered in a two-way crossover design. Muscle responses to transcranial magnetic stimulation (TMS) of the motor cortex (both experiments 1 and 2), as well as motor point stimulation of the elbow flexors (experiment 2) were assessed. Paroxetine reduced both motor cortical (P = 0.018) and motor point voluntary activation (P = 0.036) during the maximal contraction protocol. Paroxetine also reduced exercise-induced lengthening of the TMS silent period during the submaximal (P = 0.037) and maximal (P = 0.002) contraction protocols. Activation of inhibitory 5-HT1A receptors on motoneurons likely exacerbated exercise-induced reductions in voluntary drive to the elbow flexors. However, 5-HT modulation of motor activity also appeared at the supraspinal level.

DOI

10.1152/jn.00182.2022

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