A Rossi1, R Mazzocchio, B Decchi. 1. Dipartimento di Scienze Neurologiche e del Comportamento, Università degli Studi di Siena, Siena, Italy. rossiale@unisi.it
Abstract
OBJECTIVE: To test the hypothesis that 'metabolites released during fatiguing muscle contractions excite group III-IV muscle nociceptive afferents, inhibiting homonymous motoneurones via Renshaw cells,' by recording changes in recurrent inhibition of soleus motoneurones when high-threshold, small-diameter afferents (group III-IV fibres) from the same muscle were tonically activated. METHODS: Experiments were performed in 7 healthy subjects at rest and during weak isometric voluntary contraction of the soleus muscle. Muscle nociceptive afferents were activated by local standardized injection of levo-ascorbic acid. Renshaw cells were orthodromically activated by a conditioning H reflex and the resulting recurrent inhibition of the soleus motoneurones was assessed by a subsequent test H reflex. An additional H reflex of the same size as the test reflex was used to assess motoneurone excitability. RESULTS: At rest, muscle nociceptive stimulation produced transient facilitation of both test H and reference H reflexes. Under weak voluntary contraction, muscle nociceptive stimulation produced long-lasting extra-inhibition and extra-facilitation of the test reflex and reference reflex respectively, the time course of which closely resembled that of the subjective muscle pain curve. CONCLUSIONS: Discharge of putative group III-IV muscle afferents facilitated homonymous recurrent inhibition. The filtering property of recurrent inhibition may contribute to limit motoneurone activity during muscle pain and/or adapt motoneurone firing rate to the modified contractile properties of motor units as muscle fatigue developed.
OBJECTIVE: To test the hypothesis that 'metabolites released during fatiguing muscle contractions excite group III-IV muscle nociceptive afferents, inhibiting homonymous motoneurones via Renshaw cells,' by recording changes in recurrent inhibition of soleus motoneurones when high-threshold, small-diameter afferents (group III-IV fibres) from the same muscle were tonically activated. METHODS: Experiments were performed in 7 healthy subjects at rest and during weak isometric voluntary contraction of the soleus muscle. Muscle nociceptive afferents were activated by local standardized injection of levo-ascorbic acid. Renshaw cells were orthodromically activated by a conditioning H reflex and the resulting recurrent inhibition of the soleus motoneurones was assessed by a subsequent test H reflex. An additional H reflex of the same size as the test reflex was used to assess motoneurone excitability. RESULTS: At rest, muscle nociceptive stimulation produced transient facilitation of both test H and reference H reflexes. Under weak voluntary contraction, muscle nociceptive stimulation produced long-lasting extra-inhibition and extra-facilitation of the test reflex and reference reflex respectively, the time course of which closely resembled that of the subjective muscle pain curve. CONCLUSIONS: Discharge of putative group III-IV muscle afferents facilitated homonymous recurrent inhibition. The filtering property of recurrent inhibition may contribute to limit motoneurone activity during muscle pain and/or adapt motoneurone firing rate to the modified contractile properties of motor units as muscle fatigue developed.
Authors: Ivana Kalezic; Larisa A Bugaychenko; Alexander I Kostyukov; Alexander I Pilyavskii; Milos Ljubisavljevic; Uwe Windhorst; Håkan Johansson Journal: J Physiol Date: 2003-11-28 Impact factor: 5.182
Authors: A Truini; A Romaniello; P Svensson; F Galeotti; T Graven-Nielsen; K Wang; G Cruccu; L Arendt-Nielsen Journal: Exp Brain Res Date: 2006-05-30 Impact factor: 1.972
Authors: Ryan M Broxterman; Thomas J Hureau; Gwenael Layec; David E Morgan; Amber D Bledsoe; Jacob E Jessop; Markus Amann; Russell S Richardson Journal: J Physiol Date: 2018-05-08 Impact factor: 5.182