Schmelz M, Schmidt R, Ringkamp M, Forster C, Handwerker H O, Torebjörk H E
Institut für Physiologie und experimentelle Pathophysiologie, Erlangen, Germany.
Exp Brain Res. 1996 Apr;109(1):141-7. doi: 10.1007/BF00228635.
Unmyelinated cutaneous mechano-heat fibers (CMH) in the peroneal nerve of healthy human volunteers were studied by means of a "marking" technique which allows stable recordings from identified single units over extended periods. Mechanoreceptive field sizes were 105 +/- 13 mm2 in 25 units. These large receptive fields indicate extensive terminal branching of C fibers in the skin of foot and lower leg. Sensitization of CMHs was tested by assessment of thresholds for mechanical (von Frey hair) and heat stimuli before and after topical application of mustard oil (allyl isothiocyanate) and capsaicin (8-methyl-N-vanillyl-6-noneamide). While in a group of 14 CMHs the entire receptive field was treated with these irritant substances, in another group of 11 CMH units only parts of the receptive field were treated to check for signs of spreading sensitization through axon collaterals. Mustard oil application did not change mechanical thresholds, regardless of whether parts of or complete receptive fields were treated. However, mean heat thresholds dropped by 5.6 degrees C to 36.5 +/- 1.5 degrees C in completely treated receptive fields and by 5.7 degrees C to 37.3 +/- 3.4 degrees C in treated parts of receptive fields ("primary sensitization"). In contrast, heat thresholds in the nontreated parts did not change significantly (42.1 +/- 3.4 degrees C vs 41.2 +/- 3.9 degrees C), i.e. "secondary sensitization" to heat was lacking. The absence of primary sensitization to probing with von Frey hairs indicates that sensitization of insensitive C fibers and recruitment of insensitive axon collaterals may be more important for mechanical hyperalgesia than sensitization of conventional CMH units-apart from the contribution of central mechanisms. The lack of spread of sensitization to untreated parts of the receptive fields o CMHs ("secondary sensitization") indicates that this fiber group is probably not involved in any form of secondary hyperalgesia to heating.
通过一种“标记”技术对健康人类志愿者腓总神经中的无髓鞘皮肤机械热纤维（CMH）进行了研究，该技术能够在较长时间内对已识别的单个神经单元进行稳定记录。25个神经单元的机械感受野大小为105±13平方毫米。这些大的感受野表明C纤维在足部和小腿皮肤中存在广泛的终末分支。通过评估在局部应用芥子油（异硫氰酸烯丙酯）和辣椒素（8-甲基-N-香草基-6-壬酰胺）前后对机械刺激（von Frey毛发）和热刺激的阈值，来测试CMH的敏化情况。在一组14个CMH中，用这些刺激性物质处理整个感受野，而在另一组11个CMH单元中，仅处理感受野的部分区域，以检查是否有通过轴突侧支扩散敏化的迹象。无论处理的是感受野的部分区域还是整个区域，应用芥子油都不会改变机械阈值。然而，在完全处理的感受野中，平均热阈值下降了5.6摄氏度，至36.5±1.5摄氏度，在感受野的处理部分下降了5.7摄氏度，至37.3±3.4摄氏度（“初级敏化”）。相比之下，未处理部分的热阈值没有显著变化（42.1±3.4摄氏度对41.2±3.9摄氏度），即不存在对热的“次级敏化”。对von Frey毛发探测缺乏初级敏化表明，除了中枢机制的作用外，对不敏感C纤维的敏化和不敏感轴突侧支的募集对机械性痛觉过敏可能比传统CMH单元的敏化更重要。CMH感受野未处理部分缺乏敏化扩散（“次级敏化”）表明，该纤维组可能不参与任何形式的对热的次级痛觉过敏。
