Capaday C, Lavoie B A, Comeau F
Centre de recherche en neurobiologie, Université Laval, Québec, Canada.
Can J Physiol Pharmacol. 1995 Apr;73(4):436-49. doi: 10.1139/y95-056.
A conditioning (C) stimulus at group I strength was delivered during standing to the common peroneal (CP) nerve before a test (T) stimulus at several C-T intervals ranging from 0 to 150 ms. At sufficiently long C-T intervals (100-120 ms) the soleus H-reflex was strongly inhibited despite little, or no change, in the background level of EMG activity. This finding indicates that a significant portion of the inhibition occurs at a premotoneuronal level, likely via presynaptic inhibition of the Ia-afferent terminals. During standing, at C-T intervals of 100-120 ms (optimal C-T interval) a conditioning stimulus to the CP nerve of 1.5 times motor threshold (MT) intensity reduced the soleus H-reflex by an average of 45.8%(n = 14 subjects). The conditioning stimulus always produced a clear inhibition of the H-reflex during standing at these C-T intervals. The effects of this conditioning stimulus on the soleus H-reflex were then determined in the early part of the stance phase of walking. In contrast to standing, the conditioning stimulus produced little or no inhibition during the early part of the stance phase of walking (average inhibition 45.8 vs. 11.6%, n = 14 subjects). The soleus background EMG, and the soleus and tibialis anterior M-waves were essentially the same during standing and walking. Furthermore, there was no shift of the optimal C-T interval during walking. The difference in the effects of the conditioning stimulus was not due to differences in the size of the test H-reflex in each task. It appears to be due to a genuine task-dependent change in the input-output properties of the underlying spinal cord circuits. There are at least two, mutually compatible, explanations of these results. Firstly, during walking the intraspinal terminals of the afferent fibres (group Ia and Ib) conducting the conditioning volley may be presynaptically inhibited, or their input gated at the interneuronal level. Secondly, on the assumption that the conditioning stimulus is acting via the presynaptic inhibitory network in the spinal cord, it is possible that during walking this network is saturated as a result of increased central or peripheral synaptic inputs. Finally, it seems unlikely that differences in the refractoriness of the CP nerve between the tasks may be involved; the reasons for this are presented in the discussion.
在站立过程中，以I组强度的条件（C）刺激施加于腓总（CP）神经，然后在0至150毫秒的几个C-T间隔下施加测试（T）刺激。在足够长的C-T间隔（100 - 120毫秒）时，比目鱼肌H反射受到强烈抑制，尽管肌电图活动的背景水平几乎没有变化或没有变化。这一发现表明，大部分抑制发生在运动神经元前水平，可能是通过Ia传入终末的突触前抑制。在站立时，在100 - 120毫秒的C-T间隔（最佳C-T间隔）下，以1.5倍运动阈值（MT）强度对CP神经进行条件刺激，比目鱼肌H反射平均降低45.8%（n = 14名受试者）。在这些C-T间隔的站立过程中，条件刺激总是会对H反射产生明显的抑制。然后在步行站立期的早期确定这种条件刺激对比目鱼肌H反射的影响。与站立相反，在步行站立期的早期，条件刺激几乎没有产生抑制作用（平均抑制率分别为45.8%和11.6%，n = 14名受试者）。站立和步行过程中，比目鱼肌的背景肌电图以及比目鱼肌和胫前肌的M波基本相同。此外，步行过程中最佳C-T间隔没有变化。条件刺激效果的差异并非由于每个任务中测试H反射的大小不同。这似乎是由于潜在脊髓回路的输入-输出特性存在真正的任务依赖性变化。至少有两种相互兼容的对这些结果的解释。首先，在步行过程中，传导条件性冲动的传入纤维（Ia和Ib组）的脊髓内终末可能受到突触前抑制，或者它们的输入在中间神经元水平被门控。其次，假设条件刺激通过脊髓中的突触前抑制网络起作用，那么在步行过程中，由于中枢或外周突触输入增加，这个网络可能会饱和。最后，似乎不太可能涉及任务之间CP神经不应期的差异；讨论中给出了相关原因。
