Jankelowitz Stacey K, Howells James, Burke David
Medical Foundation Building - K25, The University of Sydney, NSW 2006, Australia.
J Physiol. 2007 Jun 15;581(Pt 3):927-40. doi: 10.1113/jphysiol.2006.123661. Epub 2007 Mar 15.
This study investigated whether there are changes in the excitability of motor axons in peripheral nerves of patients with corticospinal lesions, reflecting plasticity of the motoneuron due to altered descending drives and/or changes in afferent feedback. The excitability of motor and sensory axons in peripheral nerves of the affected limb of 11 patients with unilateral hemiparesis due to stroke was compared with that for the unaffected limbs and with data for 12 age-matched controls. There was significantly less accommodation to hyperpolarizing currents in motor axons on the affected side. There were small differences between the data for the unaffected side and that of the control subjects but these were not statistically significant. Other findings indicate that there was no change in resting membrane potential. There was no comparable alteration in the excitability of sensory axons. The changes in response of motor axons to hyperpolarizing currents could be reproduced in a computer model of the human motor axon by reducing the hyperpolarization-activated conductance, IH, by 30% and the quantitatively small leak conductance by 77%. The data for the uninvolved side matched the data for control subjects best when IH was increased. These findings are consistent with modulation of IH by activity. They demonstrate a change in the biophysical properties of motor axons not directly affected by the pathology and synaptically remote from the lesion, and have implications for 'trans-synaptic' changes in central nervous system pathways. In human subjects studies of motor axon properties may allow insight into processes affecting the motoneuron.
本研究调查了皮质脊髓束损伤患者周围神经中运动轴突的兴奋性是否发生变化，这反映了由于下行驱动改变和/或传入反馈变化导致的运动神经元可塑性。将11例因中风导致单侧偏瘫患者患侧肢体周围神经中运动和感觉轴突的兴奋性与未患侧肢体的兴奋性以及12名年龄匹配的对照组的数据进行了比较。患侧运动轴突对超极化电流的适应性明显降低。未患侧的数据与对照组的数据之间存在微小差异，但这些差异无统计学意义。其他研究结果表明静息膜电位没有变化。感觉轴突的兴奋性没有类似改变。通过将超极化激活电导IH降低30%，将定量较小的漏电导降低77%，在人类运动轴突的计算机模型中可以重现运动轴突对超极化电流反应的变化。当IH增加时，未受累侧的数据与对照组的数据匹配最佳。这些发现与活动对IH的调节一致。它们证明了未直接受病理影响且与病变突触距离较远的运动轴突生物物理特性的变化，并且对中枢神经系统通路中的“跨突触”变化具有影响。在人体研究中，对运动轴突特性的研究可能有助于深入了解影响运动神经元的过程。
