Wargon I, Lamy J C, Baret M, Ghanim Z, Aymard C, Pénicaud A, Katz R
Unité mixte de recherche INSERM U731, UPMC, Service de Médecine Physique et Réadaptation, Hôpital de la Salpêtrière, 75651, Paris cedex 13, France.
Exp Brain Res. 2006 Jan;168(1-2):203-17. doi: 10.1007/s00221-005-0088-9. Epub 2005 Aug 11.
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 post-stimulus 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 (non-reciprocal group I inhibition) levels. It is argued that the particular connectivity at the wrist level might correspond to some functional requirements at this ball joint.
目前的研究旨在进一步描述在人类手腕和肘部水平介导屈肌和伸肌之间双突触相互性I类抑制的中间神经元通路。在第一系列实验中，我们比较了在长时间振动旨在提高拮抗激活的Ia传入纤维的电阈值后，手腕和肘部水平相互性I类抑制的电阈值。对“条件”肌腱进行长时间振动，这显著提高了肘部水平抑制的电阈值，但在手腕水平并未改变。这些结果表明，相关中间神经元的主要输入在肘部水平起源于Ia，但在手腕水平起源于Ib。在第二系列实验中，使用空间易化方法，我们比较了分别和同时向供应同名和拮抗肌的神经中的I类传入纤维发送的两个刺激脉冲对单个自愿激活运动单位的刺激后时间直方图的影响。在手腕处，而不是肘部水平，联合刺激时同名单突触I类兴奋的峰值降低，尽管拮抗IPSP刚达到阈值。由于抑制不涉及峰值的初始时间段，因此认为这种抑制不是由于Ia终末的突触前抑制，而是可能反映了同名和拮抗刺激脉冲在介导双突触抑制的中间神经元上的汇聚。结合先前报道的反复抑制对相互抑制的影响，这些结果表明，屈肌和伸肌之间的抑制在肘部（相互性Ia抑制）和手腕（非相互性I类抑制）水平的组织方式不同。有人认为，手腕水平的特殊连接可能对应于这个球窝关节的一些功能需求。
