Lee Lu-Yuan, Shuei Lin You, Gu Qihai, Chung Eleanor, Ho Chin-Yin
Department Physiology, University of Kentucky Medical Center, Lexington, Kentucky 40536-0298, USA.
Anat Rec A Discov Mol Cell Evol Biol. 2003 Jan;270(1):17-24. doi: 10.1002/ar.a.10005.
Nonmyelinated (C-) fibers represent the majority of vagal afferents innervating the airways and lung, and play an important role in regulating the respiratory and cardiovascular functions under both normal and abnormal physiologic conditions. Studies of the relationship between the conduction velocities of the vagal afferents and their sensitivities to capsaicin and other chemical irritants reveal that C-fibers are the primary type of chemosensitive afferents in the rat lung. Furthermore, a distinct sensitivity to capsaicin and a weak response to lung inflation are the defining characteristics of these afferents. In cultured rat nodose and jugular ganglion neurons, capsaicin-sensitive cells were identified by measurement of the capsaicin-evoked calcium transients using the Fura-2-based ratiometric imaging technique. The percentage of capsaicin-sensitive neurons gradually decreases as the cell diameter increases. However, the capsaicin-sensitive neurons cannot be precisely identified solely on the basis of the cell size. Anandamide, an endogenous cannabinoid released from leukocytes and epithelial cells, consistently evokes a stimulatory effect on pulmonary C-fiber endings by activating vanilloid receptor type 1 (VR1). The discharge pattern of pulmonary C-fibers evoked by anandamide closely resembles that produced by a much lower ( approximately 1/600) dose of capsaicin in the same fibers. Whether anandamide acts as a potential endogenous ligand to VR1 at the C-fiber terminals is unclear, and the physiological role of VR1 in modulating the transduction properties of these afferents also remains to be determined.
无髓鞘（C-）纤维是支配气道和肺的迷走神经传入纤维的主要组成部分，在正常和异常生理条件下调节呼吸和心血管功能方面发挥着重要作用。对迷走神经传入纤维的传导速度与其对辣椒素和其他化学刺激物的敏感性之间关系的研究表明，C-纤维是大鼠肺中主要的化学敏感传入纤维类型。此外，对辣椒素的独特敏感性和对肺膨胀的微弱反应是这些传入纤维的特征。在培养的大鼠结状和颈静脉神经节神经元中，使用基于Fura-2的比率成像技术通过测量辣椒素诱发的钙瞬变来鉴定对辣椒素敏感的细胞。随着细胞直径的增加，对辣椒素敏感的神经元百分比逐渐降低。然而，不能仅根据细胞大小精确鉴定对辣椒素敏感的神经元。花生四烯酸乙醇胺是一种从白细胞和上皮细胞释放的内源性大麻素，通过激活1型香草酸受体（VR1）持续对肺C-纤维末梢产生刺激作用。花生四烯酸乙醇胺诱发的肺C-纤维放电模式与相同纤维中低得多（约1/600）剂量的辣椒素产生的放电模式非常相似。花生四烯酸乙醇胺是否在C-纤维末梢作为VR1的潜在内源性配体尚不清楚，VR1在调节这些传入纤维的转导特性中的生理作用也有待确定。
