Abstract: Objective To explore the mechanism by which internal heat acupuncture intervenes in peripheral sensitization of dorsal root ganglia （DRG） in chronic soft tissue pain, with a focus on the Wnt/β-catenin signaling pathway. Methods Forty-five clean-grade healthy adult New Zealand white rabbits were randomly divided into three groups （n=15）： control, model, and internal heat acupuncture group. A chronic soft tissue injury model was established using mechanical impact-induced contusion. After modeling, the acupuncture group received internal heat acupuncture once weekly for two weeks. At designated time points, spontaneous electromyographic activity frequency and spontaneous potential scores at the injured left hind limb were recorded. Local tissue thickness, color Doppler flow imaging （CDFI） signals, mean elastic modulus, and ultrasound images were also evaluated. Tissue samples were collected for histopathology, immunohistochemistry, Western blotting, and RT-PCR to assess pathological changes and the expression of vascular endothelial growth factor （VEGF）, basic fibroblast growth factor （bFGF）, brain-derived neurotrophic factor （BDNF）, and glial cell line-derived neurotrophic factor （GDNF）. In addition, the expression of Wnt pathway components,including active β-catenin, Wnt-5a, Frizzled8 protein, and their corresponding mRNAs,was assessed in the L4—L6 spinal DRG. Results In the internal heat acupuncture group, spontaneous activity frequency and potential scores were significantly lower than model group （both P<0.01）. Compared with both the pre-treatment values and the model group, the maximum thickness of the gastrocnemius, biceps femoris, and Achilles tendon in the injured area was significantly reduced （all P<0.01）, and the mean elastic modulus of the lesion also decreased markedly (P<0.01） in the acupuncture group. The expression levels of VEGF, bFGF, BDNF and GDNF in the acupuncture group were significantly lower than in the model group （all P<0.01）. Moreover, the expression of active β-catenin, Wnt-5a, Frizzled8 protein, and their mRNAs in L4-L6 DRG were significantly reduced compared with the model group （all P<0.01）. Conclusion Internal heat acupuncture exerts its analgesic effect by modulating the expression of Wnt-related signaling molecules in the L4-L6 DRG and adjusting local neurotrophic factors in chronic soft tissue lesions, thereby decreasing spontaneous muscle activity, relieving spasms, normalizing muscle tone and elasticity, promoting tissue repair, and alleviating pain.

Key words: internal heat acupuncture, peripheral sensitization, Wnt/β-catenin signaling pathway, ultrasound