Authors: I Wargon J C Lamy M Baret Z Ghanim C Aymard A Pénicaud R Katz
Publish Date: 2005/08/11
Volume: 168, Issue: 1-2, Pages: 203-217
Abstract
The present studies are designed to further characterise the interneuronal pathway mediating the disynaptic reciprocal group I inhibition between flexors and extensors at the wrist and the elbow levels in humans In the first series of experiments we compared the electrical threshold of the reciprocal group I inhibition at the wrist and the elbow level after a prolonged vibration aimed at raising the electrical threshold of the antagonistic activated Ia afferents Prolonged vibration to the ‘conditioning’ tendon which raised significantly the electrical threshold of the inhibition at the elbow level did not alter it at the wrist level These results suggest that the dominant input to the relevant interneurones is Ia in origin at the elbow level but Ib in origin at the wrist level In the second series of experiments using the spatial facilitation method we compared the effects on the poststimulus time histograms of single voluntarily activated motor units of two volleys delivered both separately and together to group I afferents in the nerves supplying the homonymous and antagonistic muscles At the wrist but not at the elbow level the peak of homonymous monosynaptic group I excitation was reduced on combined stimulation although the antagonistic IPSP was just at the threshold Because the suppression did not involve the initial bins of the peak it is argued that the suppression is not due to presynaptic inhibition of Ia terminals but probably reflects convergence between the homonymous and antagonistic volleys onto the interneurones mediating the disynaptic inhibition Taken together with the previously reported effects of recurrent inhibition on reciprocal inhibition these results suggest that inhibition between flexors and extensors is differently organised at the elbow reciprocal Ia inhibition and the wrist nonreciprocal group I inhibition levels It is argued that the particular connectivity at the wrist level might correspond to some functional requirements at this ball jointThe authors wish to express their gratitude to Professor E PierrotDeseilligny for reading and commenting upon the manuscript Our thanks are also due to M Dodo for her unfailing assistance during the course of the experiments and G Bard for typing the manuscript This work was supported by grants from APHP INSERM and MESR unité de recherche mixte INSERM U731 UPMC IRME and Institut Garches Zaid Ghanim was supported by Ministère des Affaires Etrangères
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