Heppelmann B, Gallar J, Trost B, Schmidt R F, Belmonte C
Physiologisches Institut der Universität Würzburg, Röntgenring 9, D-97070 Würzburg, Germany.
J Comp Neurol. 2001 Dec 10;441(2):148-54. doi: 10.1002/cne.1403.
Sensory endings that respond to local cooling were identified electrophysiologically in the cat's sclera. Functionally identified scleral thermal fibers were then used to analyze the structural characteristics of cold receptor endings. Four Adelta units sensitive to controlled cooling of their scleral receptive fields were recorded. The receptive areas were mapped, demarcated with pins and examined electron microscopically using extensive three-dimensional reconstructions. The supporting tissue within the receptive areas of cold units consisted of dense collageneous tissue with a small number of blood vessels that were either veins or capillaries. Adelta nerve fibers were found within these tissue blocks presumably corresponding with cold sensitive fibers. Small nerves and single nerve fibers devoid of a perineurium were found in all parts of the tissue, only occasionally passing a blood vessel. The terminal portions showed axonal swellings all along the unmyelinated segment filled with mitochondria, glycogen particles, and some vesicles. About 30% of the terminal axonal membrane is not covered by Schwann cells. In the unmyelinated distal portion, the mitochondrial content ranged from 0.012 to 0.038 microm(3) mitochondrial volume per microm(2) nerve fiber membrane. In comparison with sensory endings in the cat's knee joint, cold receptors in the cat sclera showed many similarities in their three-dimensional structure with polymodal nociceptor endings of the knee joint but contain less mitochondria. This suggests that cold sensory endings do not require specialized cellular processes for the transduction of cold stimuli, as is the case for multimodal transduction and sensitization in the terminal portion of polymodal nociceptors.
通过电生理学方法在猫的巩膜中识别出对局部冷却有反应的感觉末梢。然后，利用功能已明确的巩膜热纤维来分析冷感受器末梢的结构特征。记录了4个对其巩膜感受野的控制性冷却敏感的Aδ单位。绘制了感受区域图，用大头针进行标记，并通过广泛的三维重建进行电子显微镜检查。冷感受器单位感受区域内的支持组织由致密的胶原组织组成，其中有少量的静脉或毛细血管。在这些组织块中发现了Aδ神经纤维，推测它们与冷敏感纤维相对应。在组织的所有部位都发现了没有神经束膜的小神经和单根神经纤维，它们只是偶尔穿过血管。末梢部分在整个无髓鞘段都显示出轴突肿胀，充满了线粒体、糖原颗粒和一些小泡。约30%的末梢轴突膜没有施万细胞覆盖。在无髓鞘的远端部分，线粒体含量为每平方微米神经纤维膜0.012至0.038立方微米线粒体体积。与猫膝关节中的感觉末梢相比，猫巩膜中的冷感受器在三维结构上与膝关节的多模式伤害感受器末梢有许多相似之处，但线粒体含量较少。这表明冷感觉末梢不像多模式伤害感受器末梢的终末部分那样，在冷刺激转导方面不需要特殊的细胞过程，多模式伤害感受器末梢存在多模式转导和敏化现象。
