Document Detail

Spinal Opioid Receptor-Sensitive Muscle Afferents Contribute to the Fatigue-Induced Increase in Intracortical Inhibition in Healthy Humans.
MedLine Citation:
PMID:  21317218     Owner:  NLM     Status:  Publisher    
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 the 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 (0.025 mg/ml) blocking the central projection of spinal opioid receptor-sensitive lower limb muscle afferents. To quantify exercise-induced peripheral fatigue, quadriceps twitch force (Qtw,pot) was assessed via supramaximal magnetic femoral nerve stimulation before and after exercise. Motor evoked potentials (MEP) and cortical silent periods (CSP) were evaluated via transcranial magnetic stimulation (TMS) 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 (Qtw,pot: -35% and -39% for placebo and fentanyl, respectively; P=0.38). Immediately following exercise on both days, MEPs were similar to those obtained prior to exercise. Compared to pre-exercise baseline, CSP in the placebo trial was 21±5% longer post-exercise (P<0.01). In contrast, CSP following the fentanyl trial was not significantly prolonged compared to 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 allude that spinal opioid receptor-sensitive muscle afferents might influence central fatigue by facilitating intracortical inhibition.
Lea Hilty; Kai Lutz; Konrad Maurer; Tobias Rodenkirch; Christina M Spengler; Urs Boutellier; Lutz Jäncke; Markus Amann
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-2-11
Journal Detail:
Title:  Experimental physiology     Volume:  -     ISSN:  1469-445X     ISO Abbreviation:  -     Publication Date:  2011 Feb 
Date Detail:
Created Date:  2011-2-14     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9002940     Medline TA:  Exp Physiol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
1 ETH Zürich and University of Zürich;
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