Electroacupuncture Relieves Fibromyalgia Pain in a Female Mouse Model by Augmenting Cannabinoid Receptor 1 Expression and Suppressing Astrocyte and Microglial Activation in Nociceptive Pathways

Background/Objectives: Fibromyalgia is a chronic pain syndrome with unclear etiology, meaning that it is difficult to treat effectively. The stimulation of cannabinoid receptor 1 (CB1) suppresses neuronal excitability and synaptic transmission in nociceptive pathways via reducing activity in the calcium channel and promoting the opening of the potassium channel. Methods: In this study, we examined whether CB1 activity contributes to the antinociceptive efficacy of electroacupuncture (EA) in a mouse fibromyalgia (FM) pain model established using intermittent cold stress (ICS). The model mice demonstrated both mechanical and thermal hyperalgesia measured using the von Frey and Hargreaves tests, respectively. Results: Electroacupuncture effectively reduced both forms of hyperalgesia and enhanced CB1 expression in the dorsal root ganglia, spinal cord, hypothalamus, and periaqueductal gray. In addition, EA attenuated the fibromyalgia-associated reactive transformation of microglia and astrocytes and the activation of the pain-related TLR4–MyD88–TRAF6 signaling pathway. The effects of ICS were also mitigated by the deletion of Trpv1, the gene encoding the transient receptor potential cation channel TRPV1 (capsaicin channel) implicated in nociceptive and inflammatory signaling. Further, the antinociceptive efficacy of EA was partially recapitulated by the acupoint injection of a CB1 agonist and abolished by the injection of a CB1 antagonist, suggesting that activating CB1 is essential for this therapeutic effect. Conclusions: Electroacupuncture can effectively alleviate mechanical and thermal hyperalgesia in a mouse model affected by fibromyalgia pain by activating the CB1 pathway, highlighting the therapeutic potential of CB1 agonism as a therapeutic strategy.