Cutaneous Hypersensitivity as an Indicator of Visceral Inflammation via C-Nociceptor Axon Bifurcation
Yehong Fang 1,3 • Shu Han 2 • Xiaoxue Li 2 • Yikuan Xie 1,3 • Bing Zhu 2 • Xinyan Gao 2 • Chao Ma 1,3
1 Institute of Basic Medical Sciences, Department of Human Anatomy, Histology and Embryology, Neuroscience Center, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing 100005, China
2 Department of Physiology, Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing 100700, China
3 Joint Laboratory of Anesthesia and Pain, Peking Union Medical College, Beijing 100730, China
Pain on the body surface can accompany disorders in the deep tissue or internal organs. However, the anatomical and physiological mechanisms are obscure. Here, we provided direct evidence of axon bifurcation in primary C-nociceptive neurons that innervate both the skin and a visceral organ. Double-labeled dorsal root ganglion (DRG) neurons and Evans blue extravasation were observed in 3 types of chemically-induced visceral inflammation (colitis, urocystitis, and acute gastritis) rat models. In the colitis model, mechanical hypersensitivity and spontaneous activity were recorded in vivo from double-labeled C-nociceptive neurons in S1 or L6 DRGs. These neurons showed significantly enhanced responses to both somatic stimulation and colorectal distension. Our findings suggest that the branching of C-nociceptor axons contribute to cutaneous hypersensitivity in visceral inflammation. Cutaneous hypersensitivity on certain locations of the body surface might serve as an indicator of pathological conditions in the corresponding visceral organ.
Visceral inflammation; Cutaneous hypersensitivity; Axon bifurcation; C-nociceptor