Low-frequency electroacupuncture alleviates neuropathic pain via cannabinoid receptor type 2 signaling in the spinal cord dorsal horn.

OBJECTIVE: This study investigated the role of the cannabinoid receptor type 2 (CB2R) in the spinal cord dorsal horn (SCDH) using a spared nerve injury (SNI) model of neuropathic pain (NP). The aim was to clarify the analgesic effects of different electroacupuncture (EA) frequencies in SNI rats and to explore whether the higher frequency exerts analgesic effects by modulating the CB2R signaling pathway.

METHODS: An SNI rat model was initially established. Mechanical allodynia was assessed using the paw withdrawal threshold (PWT), and motor function was assessed using a gait analysis system. Expression levels of CB2R, phosphorylated p38 mitogen-activated protein kinase (p-p38 MAPK), cluster of differentiation 11b (CD11b), ionized calcium-binding adapter molecule 1 (Iba1), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were quantified via immunofluorescence staining and Western blot analysis. The functional role of the CB2R/p38 MAPK pathway was further investigated through intrathecal administration of the CB2R agonist AM1241 and the p38 MAPK inhibitor SB203580. The analgesic effects of low (2 Hz) and high-frequency (100 Hz) EA were observed in SNI rats, and the modulatory effect of the superior frequency (2 Hz) on this pathway was explored. The CB2R antagonist AM630 was co-administered with low-frequency EA to evaluate its impact on pathway activity.

RESULTS: CB2R and p-p38 MAPK expression increased after SNI and they were mainly expressed in microglia. The SNI group exhibited a substantial increase in Iba1 and CD11b staining intensity, indicating robust microglial activation, along with elevated levels of the pro-inflammatory cytokine IL-6. Intrathecal administration of either the CB2R agonist AM1241 or the p-p38 MAPK inhibitor SB203580 increased the PWT, inhibited microglial activation and decreased the release of inflammatory cytokines in the SCDH. Both low and high-frequency EA were effective in alleviating pain induced by SNI. Low-frequency EA was significantly more effective than high-frequency EA in improving PWT. Low-frequency EA improves SNI-induced gait disturbances. Low-frequency EA ameliorated hyperalgesia in SNI rats by enhancing CB2R expression and suppressing p-p38 MAPK activation. AM630 reversed this analgesic effect. Moreover, EA attenuated microglial activation and lowered the levels of pro-inflammatory cytokines, specifically TNF-α and IL-6, in the SCDH. It also suppressed the phosphorylation of phosphatidylinositol 3-kinase (PI3K) and protein kinase B (AKT). Notably, CB2R antagonism abolished all these effects.

CONCLUSION: CB2R participates in SNI-induced NP by activating the p38 MAPK pathway. Low-frequency EA shows superior efficacy compared with high-frequency EA and alleviates NP through CB2R-mediated suppression of the p38 MAPK and PI3K/AKT signaling in the SCDH. Please cite this article as: Wei ZY, Zhang JJ, Lin C, Li SY, Kang YR, Liang JQ, Liu ZQ, He XF, Shao XM, Fang JQ, Jiang YL. Low-Frequency electroacupuncture alleviates neuropathic pain via cannabinoid receptor type 2 signaling in the spinal cord dorsal horn. J Integr Med. 2026; 24(5):753-768.