Spinal opioid receptor-sensitive muscle afferents contribute to the fatigue-induced increase in intracortical inhibition in healthy humans

Lea Hilty, Kai Lutz, Konrad Maurer, Tobias Rodenkirch, Christina M Spengler, Urs Boutellier, Lutz Jäncke, Markus Amann
Experimental Physiology 2011, 96 (5): 505-17
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.

Full Text Links

Find Full Text Links for this Article


You are not logged in. Sign Up or Log In to join the discussion.

Related Papers

Remove bar
Read by QxMD icon Read

Save your favorite articles in one place with a free QxMD account.


Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"