The review surveys various aspects of the plasticity of nerve fibres, in particular the prolonged increase in their excitability evoked by polarization, focusing on a long-lasting increase in the excitability of myelinated afferent fibres traversing the dorsal columns of the spinal cord. We review the evidence that increased axonal excitability (i) follows epidurally applied direct current as well as relatively short (5 or 10 ms) current pulses and synaptically evoked intrinsic field potentials; (ii) critically depends on the polarization of branching regions of afferent fibres at the sites where they bifurcate and give off axon collaterals entering the spinal grey matter in conjunction with actions of extrasynaptic GABA_A membrane receptors; and (iii) shares the feature of being activity-independent with the short-lasting effects of polarization of peripheral nerve fibres. A comparison between the polarization evoked sustained increase in the excitability of dorsal column fibres and spinal motoneurons (plateau potentials) indicates the possibility that they are mediated by partly similar membrane channels (including non-inactivating type L Cav⁺⁺ 1.3 but not Na+ channels) and partly different mechanisms. We finally consider under which conditions trans-spinally applied DC (tsDCS) might reproduce the effects of epidural polarization on dorsal column fibres and the possible advantages of increased excitability of afferent fibres for the rehabilitation of motor and sensory functions after spinal cord injuries.

中文翻译：

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神经纤维的可塑性：传入纤维极化的长期影响

该综述调查了神经纤维可塑性的各个方面，特别是极化引起的兴奋性的长期增加，重点关注穿过脊髓背柱的有髓传入纤维的兴奋性的长期增加。我们回顾了轴突兴奋性增加的证据（i）在硬膜外施加的直流电以及相对短（5 或 10 ms）的电流脉冲和突触诱发的固有场电位之后；(ii) 严重依赖于传入纤维分支区域在它们分叉并释放轴突侧枝进入脊髓灰质的部位的极化以及突触外 GABA _{A 的作用}膜受体；(iii) 与周围神经纤维极化的短暂影响具有活动无关的特点。极化引起的背柱纤维和脊髓运动神经元（高原电位）兴奋性持续增加之间的比较表明它们可能由部分相似的膜通道介导（包括非失活型 L Cav ⁺⁺ 1.3 但不是 Na+ 通道）和部分不同的机制。我们最终考虑在哪些条件下经脊髓应用 DC (tsDCS) 可能重现硬膜外极化对背柱纤维的影响，以及增加传入纤维兴奋性对脊髓损伤后运动和感觉功能康复的可能优势。