Physiologisches Institut, Christian-Albrechts-Universität zu Kiel, Kiel, Germany.
Eur J Neurosci. 2011 Jan;33(1):110-8. doi: 10.1111/j.1460-9568.2010.07471.x. Epub 2010 Nov 3.
We hypothesized that cutaneous afferent myelinated fibers (A-fibers) and afferent unmyelinated fibers (C-fibers) respond to the same natural stimuli applied to their axons as to their terminals in the skin. In anesthetized rats, activity was recorded from afferent axons in strands isolated proximally from the sural nerve. Mechanical, cold or heat stimuli were applied to the skin or along a 15-mm length of the distal sural nerve. One-hundred and eighteen A-fibers and 109 C-fibers were characterized by their conduction velocity and/or shape of their action potentials, and by their responses to natural stimulation of the skin. Then, these fibers were tested for their responses to the same stimuli applied to the nerve. In some cases, the nerve was crushed distally after the nerve fibers had been characterized by their responses to physiological stimulation of the skin, and the responses to stimuli applied to the nerve proximal to the lesion were tested again. Almost all non-nociceptive cold-sensitive (type 1) C-fibers (97%) could be activated by cold stimuli applied to the nerve. Of nociceptive cold-sensitive (type 2) C-fibers, 39% were activated by cold stimuli applied to the nerve. Furthermore, 34% of heat-sensitive C-fibers could be activated by heating the nerve. In contrast, only 2-4% of mechanosensitive A-fibers and C-fibers responded to mechanical stimuli applied to the nerve. In conclusion, cold and heat sensitivity of cutaneous afferent neurons is not restricted to their terminals in the skin, but often extends along the axons in the nerve. Mechanosensitivity is restricted to the afferent endings in the skin.
我们假设皮肤传入有髓纤维（A 纤维）和传入无髓纤维（C 纤维）对施加在其轴突上的相同自然刺激与施加在其皮肤末端的刺激做出相同的反应。在麻醉大鼠中，从近段分离的腓肠神经束中记录传入轴突的活动。机械、冷或热刺激施加于皮肤或沿 15mm 长的腓肠神经远端。用其传导速度和/或动作电位的形状，以及对皮肤自然刺激的反应来对 118 个 A 纤维和 109 个 C 纤维进行特征描述。然后，对这些纤维进行相同刺激施加于神经的反应测试。在某些情况下，在通过纤维对皮肤生理刺激的反应来特征描述神经纤维之后，在神经末梢处对神经进行压迫，然后再次测试对施加于神经近端的刺激的反应。几乎所有非伤害性冷敏感（1 型）C 纤维（97%）都可以通过施加于神经的冷刺激来激活。伤害性冷敏感（2 型）C 纤维中，有 39%可以通过施加于神经的冷刺激来激活。此外，34%的热敏感 C 纤维可以通过加热神经来激活。相比之下，只有 2-4%的机械敏感 A 纤维和 C 纤维对施加于神经的机械刺激有反应。总之，皮肤传入神经元的冷觉和热觉敏感性不仅限于其皮肤末端，而且常常沿神经轴突延伸。机械敏感性仅限于皮肤传入末梢。
