Electroacupuncture relieved visceral and referred hindpaw hypersensitivity in colitis rats by inhibiting tyrosine hydroxylase expression in the sixth lumbar dorsal root ganglia.

Irritable bowel syndrome patients frequently complain of pain in body regions somatotopically distinct from the gut, suggesting the involvement of an exaggerated signaling process in both visceral and somatic sensory pathways. Increasing evidence has shown that sprouting of tyrosine hydroxylase immunoreactive (TH-IR) fibers toward sensory neurons in dorsal root ganglia maintains and exacerbates the neuropathic and inflammatory pain, as well as colonic inflammation. The aim of the present study was to determine whether electroacupuncture could alleviate the visceral and secondary somatic hyperalgesia in colitis rats by suppressing the TH-IR expression in related dorsal root ganglia. After trinitrobenzene sulfonic acid irritation, rats developed inflammatory tissue damage in the distal colon, which was accompanied by visceral hypersensitivity and secondary hind paw hyperalgesia, as indicated by enhanced visceromotor response to colorectal distension and decreased mechanical and thermal withdrawal latency of the hind paw. Additionally, excessive TH-IR fibers sprouted toward calcitonin gene-related peptide immunoreactive sensory neurons, and TH-IR neurons also increased in the sixth lumbar dorsal root ganglia of colitis rats. Both electroacupuncture and guanethidine attenuated visceral and referred hind paw hyperalgesia by inhibiting the over-expression of TH-IR neurons and fibers in the sixth lumbar dorsal root ganglia. Moreover local inflammatory damage in the distal colon was restored after 7 days of electroacupuncture intervention. These results suggest that electroacupuncture relieved visceral and referred hind paw hypersensitivity in colitis rats by inhibiting TH expression in the sixth lumbar dorsal root ganglia.