[Study on the mechanism of ankle-three-needle acupuncture inhibiting radicular neuralgia by regulating macrophage polarization and inflammation through 5-HT].

Objective To investigate the mechanism by which Ankle-Three-Needle (ATN) acupuncture alleviates radicular neuropathic pain (RNP) through modulation of pain thresholds and inflammatory responses via 5-hydroxytryptamine (5-HT) signaling. Methods Male Sprague-Dawley (SD) rats were randomly assigned to four groups: sham-operated group, model group, ATN group, and conventional acupuncture group. A rat model of radicular neuropathic pain was established, and corresponding treatments were administered according to group allocation. Pain threshold alterations were assessed using the acetone test, hot plate test, and von Frey filament test. The levels of 5-hydroxytryptamine (5-HT), β-endorphin (β-EP), and substance P (SP) in serum and brain tissues were quantified by enzyme-linked immunosorbent assay (ELISA). Macrophage polarization at the site of sciatic nerve injury and the expression of inflammatory cytokines were analyzed using quantitative real-time PCR (qRT-PCR) and flow cytometry. Rescue experiments involving activation of the 5-HT3 receptor were conducted to elucidate the role of 5-HT signaling in ATN-mediated modulation of pain thresholds and inflammatory responses. Results ATN treatment significantly increased pain thresholds in rats with radicular neuropathic pain, alleviated pain-related behaviors, and inhibited M1 macrophage polarization as well as pro-inflammatory responses at the injury site. Neurochemical analyses demonstrated that ATN upregulated 5-HT levels in the brain while reducing serum 5-HT concentrations. Rescue experiments further confirmed that both 5-HT and the 5-HT3 receptor are essential mediators of ATN-induced regulation of pain thresholds and inflammatory cytokine expression. Conclusion Ankle-Three-Needle acupuncture effectively alleviates radicular neuropathic pain by decreasing serum 5-HT levels and modulating 5-HT3 receptor-mediated macrophage M1/M2 polarization and inflammatory cytokine expression.