Guissard N, Duchateau J, Hainaut K
Laboratory of Biology, Université Libre de Bruxelles, 28 avenue P. Héger, CP 168, 1000 Brussels, Belgium.
Exp Brain Res. 2001 Mar;137(2):163-9. doi: 10.1007/s002210000648.
The effect of pre- versus postsynaptic mechanisms in the decrease in spinal reflex response during passive muscle stretching was studied. The change in the electromyographic (EMG) responses of two reflex pathways sharing a common pool of motoneurones, with (Hoffmann or H reflex) or without (exteroceptive or E reflex) a presynaptic inhibitory mechanism, was compared. The EMG activities were recorded in the soleus muscle in response to the electrical stimulation of the tibial nerve at the popliteal fossa (H reflex), and at the ankle (E reflex) for different dorsiflexion angles of the ankle. The compound muscle action potential (M wave) in the soleus and the abductor hallucis was recorded in order to control the stability of the electrical stimulation during stretching. The results indicate that in the case of small-amplitude muscle stretching (10 degrees of dorsiflexion), a significant reduction (-25%; P < 0.05) in the Hmax/Mmax ratio was present without any significant change in the Emax/Mmax ratio. At a greater stretching amplitude (20 degrees of dorsiflexion), the E reflex was found to be reduced (-54.6%; P < 0.001) to a similar extent as the H reflex (-54.2%). As soon as the ankle joint returned to the neutral position (ankle at 90 degrees), the two reflex responses recovered their initial values. In additional experiments, motor-evoked potential (MEP) induced by the magnetic stimulation of the motor cortex was recorded and showed a similar type of behaviour to that observed in the E reflex. These results indicate that reduced motoneurone excitation during stretching is caused by pre- and postsynaptic mechanisms. Whereas premotoneuronal mechanisms are mainly involved in the case of small stretching amplitude, postsynaptic ones play a dominant role in the reflex inhibition when larger stretching amplitude is performed.
研究了被动肌肉拉伸过程中突触前与突触后机制对脊髓反射反应降低的影响。比较了共享一个运动神经元共同池的两条反射通路的肌电图（EMG）反应变化，其中一条有（霍夫曼或H反射）而另一条没有（外感受性或E反射）突触前抑制机制。在比目鱼肌中记录EMG活动，以响应在腘窝处对胫神经的电刺激（H反射），以及在踝关节处对不同背屈角度的电刺激（E反射）。记录比目鱼肌和拇展肌中的复合肌肉动作电位（M波），以控制拉伸过程中电刺激的稳定性。结果表明，在小幅度肌肉拉伸（背屈10度）的情况下，Hmax/Mmax比值显著降低（-25%；P<0.05），而Emax/Mmax比值没有任何显著变化。在更大的拉伸幅度（背屈20度）下，发现E反射降低（-54.6%；P<0.001），程度与H反射（-54.2%）相似。一旦踝关节恢复到中立位置（踝关节处于90度），两种反射反应恢复到初始值。在额外的实验中，记录了由运动皮层磁刺激诱发的运动诱发电位（MEP），其表现出与E反射中观察到的类似行为类型。这些结果表明，拉伸过程中运动神经元兴奋的降低是由突触前和突触后机制引起的。在小拉伸幅度的情况下，主要涉及运动神经元前机制，而在进行较大拉伸幅度时突触后机制在反射抑制中起主导作用。
