MacIver M B, Tanelian D L
Department of Anesthesia, Stanford University School of Medicine, California 94305-5117.
J Neurosci. 1993 Oct;13(10):4511-24. doi: 10.1523/JNEUROSCI.13-10-04511.1993.
An in vitro preparation of rabbit cornea was used to compare anatomical specialization and electrophysiological responses of A delta and C fiber sensory afferents which terminate as free nerve endings. Living nerve endings were visualized using epifluorescence microscopy and the vital dye 4-di2-ASP, and response properties were determined using microstimulation and recording of fiber discharge activity. Fiber type was determined based on conduction velocity measurement and preferred stimulus energy (modality) of each fiber. Four modality-specific fiber populations were identified: (1) slowly adapting C fiber cold receptors (conduction velocity of 0.25-1.6 m/sec), (2) C fiber chemosensitive units with mixed phasic and tonic activity (1.1-1.8 m/sec), (3) rapidly adapting mechanosensitive A delta fibers (1.5-2.8 m/sec), and (4) high-threshold mechano/heat (> 350 dyne or > 40 degrees C) phasic A delta afferents (3.5-4.4 m/sec). In addition to these physiological differences, anatomical specialization was also noted. A delta fiber nerve endings were distinguished from those of C fibers by thin, elongated sensory endings that ran parallel to the corneal surface; C fiber endings formed short, branching clusters that ran mostly perpendicular to the surface. The elongated structure of A delta nerve endings was associated with directional selectivity for mechanical stimuli. These results substantiate previous suggestions that free nerve endings can exhibit both structural and functional specialization.
利用兔角膜的体外制备物，比较了作为游离神经末梢终止的Aδ和C纤维感觉传入神经的解剖学特化和电生理反应。使用落射荧光显微镜和活性染料4-di2-ASP对活神经末梢进行可视化，并使用微刺激和记录纤维放电活动来确定反应特性。根据每个纤维的传导速度测量和偏好的刺激能量（模态）来确定纤维类型。鉴定出四个模态特异性纤维群体：(1) 慢适应性C纤维冷感受器（传导速度为0.25 - 1.6米/秒），(2) 具有混合性时相和紧张性活动的C纤维化学敏感单位（1.1 - 1.8米/秒），(3) 快适应性机械敏感Aδ纤维（1.5 - 2.8米/秒），以及(4) 高阈值机械/热觉（> 350达因或 > 40摄氏度）时相性Aδ传入神经（3.5 - 4.4米/秒）。除了这些生理差异外，还注意到了解剖学特化。Aδ纤维神经末梢与C纤维神经末梢的区别在于，Aδ纤维的感觉末梢细而长，与角膜表面平行；C纤维末梢形成短的分支簇，大多与表面垂直。Aδ神经末梢的细长结构与对机械刺激的方向选择性有关。这些结果证实了先前的推测，即游离神经末梢可以表现出结构和功能特化。
