Department of Anatomy and Neuroscience, The University of Melbourne, Melbourne, Victoria, Australia.
PLoS One. 2018 Mar 28;13(3):e0195108. doi: 10.1371/journal.pone.0195108. eCollection 2018.
It is generally believed that the unencapsulated sensory nerve terminals of modality specific C- and Aδ-neurons lack structural specialization. Here we determined the morphology of functionally defined polymodal receptors and cold thermoreceptors in the guinea pig corneal epithelium. Polymodal receptors and cold thermoreceptors were identified by extracellular recording at the surface of the corneal epithelium. After marking the recording sites, corneas were processed to reveal immunoreactivity for the transient receptor potential channels TRPV1 (transient receptor potential cation channel, subfamily V, member 1) or TPRM8 (transient receptor potential cation channel subfamily M member 8). Polymodal receptor nerve terminals (n = 6) were TRPV1-immunoreactive and derived from an axon that ascended from the sub-basal plexus to the squamous cell layer where it branched into fibers that ran parallel to the corneal surface and terminated with small bulbar endings (ramifying endings). Cold thermoreceptor nerve terminals were TRPM8-immunoreactive (n = 6) and originated from an axon that branched as it ascended through the wing cell and squamous cell layers and terminated with large bulbar endings (complex endings). These findings indicate that modality specific corneal sensory neurons with unencapsulated nerve endings have distinct nerve terminal morphologies that are likely to relate to their function.
人们普遍认为，无囊包裹的模态特异性 C 纤维和 Aδ 纤维感觉神经末梢缺乏结构特化。在这里，我们确定了豚鼠角膜上皮中功能定义的多模态感受器和冷热敏感受器的形态。通过在角膜上皮表面进行细胞外记录来识别多模态感受器和冷热敏感受器。在标记记录部位后，对角膜进行处理以显示对瞬时受体电位通道 TRPV1（瞬时受体电位阳离子通道，亚家族 V，成员 1）或 TPRM8（瞬时受体电位阳离子通道亚家族 M 成员 8）的免疫反应性。多模态感受器神经末梢（n = 6）为 TRPV1 免疫反应性，源自从基底下丛上升到鳞状细胞层的轴突，在那里它分支成与角膜表面平行运行并以小球状末端（分支末端）结束的纤维。冷热敏感受器神经末梢为 TRPM8 免疫反应性（n = 6），起源于上升穿过翼状细胞和鳞状细胞层的轴突，并以大的小球状末端（复杂末端）结束。这些发现表明，具有无囊包裹神经末梢的特定模态角膜感觉神经元具有独特的神经末梢形态，这可能与其功能有关。
