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Hilty, L; Lutz, K; Maurer, K; Rodenkirch, T; Spengler, C M; Boutellier, U; Jäncke, L; Amann, M (2011). Spinal opioid receptor-sensitive muscle afferents contribute to the fatigue-induced increase in intracortical inhibition in healthy humans. Experimental Physiology, 96(5):505-517.

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Abstract

We investigated the influence of spinal opioid receptor-sensitive muscle afferents on cortical changes following fatiguing unilateral knee-extensor exercise. On separate days, seven subjects performed an identical five sets of intermittent isometric right-quadriceps contractions, each consisting of eight submaximal contractions [63 ± 7% maximal voluntary contraction (MVC)] and one MVC. The exercise was performed following either lumbar interspinous saline injection or lumbar intrathecal fentanyl injection blocking the central projection of spinal opioid receptor-sensitive lower limb muscle afferents. To quantify exercise-induced peripheral fatigue, quadriceps twitch force (Q(tw,pot)) was assessed via supramaximal magnetic femoral nerve stimulation before and after exercise. Motor evoked potentials and cortical silent periods (CSPs) were evaluated via transcranial magnetic stimulation of the motor cortex during a 3% MVC pre-activation period immediately following exercise. End-exercise quadriceps fatigue was significant and similar in both conditions (Q(tw,pot) -35 and -39% for placebo and fentanyl, respectively; P = 0.38). Immediately following exercise on both days, motor evoked potentials were similar to those obtained prior to exercise. Compared with pre-exercise baseline, CSP in the placebo trial was 21 ± 5% longer postexercise (P < 0.01). In contrast, CSP following the fentanyl trial was not significantly prolonged compared with the pre-exercise baseline (6 ± 4%). Our findings suggest that the central effects of spinal opioid receptor-sensitive muscle afferents might facilitate the fatigue-induced increase in CSP. Furthermore, since the CSP is thought to reflect inhibitory intracortical interneuron activity, which may contribute to central fatigue, our findings imply that spinal opioid receptor-sensitive muscle afferents might influence central fatigue by facilitating intracortical inhibition.

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17 citations in Web of Science®
18 citations in Scopus®
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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Institute of Physiology
07 Faculty of Science > Institute of Physiology

06 Faculty of Arts > Institute of Psychology
04 Faculty of Medicine > University Hospital Zurich > Institute of Anesthesiology
DDC:570 Life sciences; biology
150 Psychology
610 Medicine & health
Language:English
Date:2011
Deposited On:26 Oct 2011 10:06
Last Modified:27 Nov 2013 18:36
Publisher:Wiley-Blackwell
ISSN:0958-0670
Publisher DOI:10.1113/expphysiol.2010.056226
PubMed ID:21317218

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