The excitability of large nerve fibers is reduced when their membrane potential is slowly depolarizing, i.e. the fibers display accommodation. The aim of this study was to assess accommodation in small (mainly Aδ) and large (Aβ) cutaneous sensory nerve fibers using the perception threshold tracking (PTT) technique. Linearly increasing ramp currents (1 ms -200 ms) were used to assess the excitability of the nerve fibers by cutaneous electrical stimulation. To investigate the PPT technique's ability to preferentially activate different fiber types, topical application of lidocaine/prilocaine (EMLA) or a placebo cream was applied. By means of computational modelling, the underlying mechanisms governing the perception threshold in the two fiber types was studied. The axon models included the voltage-gated ion channels: Na_TTXs, Na_TTXr, Na_P, K_Dr, K_M, and HCN. Large fibers displayed accommodation, whereas small fibers did not display accommodation (p<0.05). For the pin electrode, a significant interaction was observed between cream (EMLA or placebo) and pulse duration (p<0.05) whereas for the patch electrode, there was no significant interaction between cream and duration which supports the pin electrode's preferential activation of small fibers. The results from the computational model suggested that differences in accommodation between the two fiber types may originate from selective expression of voltage-gated ion channels, particularly the transient Na_TTXr and/or K_Dr. e PTT technique could assess the excitability changes during accommodation in different nerve fibers. Therefore, the PTT technique may be a useful tool for studying excitability in nerve fibers both in healthy as well as in pathological conditions.

中文翻译：

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小的和大的皮肤纤维对缓慢增加的斜坡脉冲显示不同的兴奋性。

当它们的膜电位缓慢去极化时，大神经纤维的兴奋性降低，即纤维显示调节。本研究的目的是使用感知阈值跟踪 (PTT) 技术评估小 (主要是 Aδ) 和大 (Aβ) 皮肤感觉神经纤维的调节。线性增加的斜坡电流 (1 ms -200 ms) 用于通过皮肤电刺激评估神经纤维的兴奋性。为了研究 PPT 技术优先激活不同纤维类型的能力，局部应用利多卡因/丙胺卡因 (EMLA) 或安慰剂乳膏。通过计算建模，研究了控制两种纤维类型感知阈值的潜在机制。轴突模型包括电压门控离子通道：Na _TTXs、Na _TTXr、Na _P、K _Dr、K _M和 HCN。大纤维显示调节，而小纤维不显示调节（p<0.05）。对于针电极，在乳膏（EMLA 或安慰剂）和脉冲持续时间（p<0.05）之间观察到显着的相互作用，而对于贴片电极，乳膏和持续时间之间没有显着的相互作用，这支持针电极优先激活小纤维. 计算模型的结果表明，两种纤维类型之间的调节差异可能源于电压门控离子通道的选择性表达，特别是瞬态 Na _TTXr和/或 K _Dr. e PTT 技术可以评估不同神经纤维在调节过程中的兴奋性变化。因此，PTT 技术可能是研究健康和病理状态下神经纤维兴奋性的有用工具。