Analgesia with 5' extracellular nucleotidase-mediated electroacupuncture for neuropathic pain

Background: Acupuncture is a treatment for neuropathic pain, but its mechanism remains unclear. Previous studies showed that analgesia was induced in rats with neuropathic pain when their spinal cord adenosine content increased after electroacupuncture (EA); however, the mechanism behind this electroacupuncture-induced increase has not been clarified. Objective: This study aimed to determine the role that ecto-5'-nucleotidase plays in EA-induced analgesia for neuropathic pain. Methods: We performed electroacupuncture at the Zusanli acupoint on the seventh day after establishing a rat model of neuropathic pain induced through chronic constriction injuries. We observed the mechanical withdrawal threshold and thermal pain threshold and detected the expression of ecto-5'-nucleotidase in the spinal cord using Western blot. Chronic constriction injury rat models were intraperitoneally injected with a,f3-methyleneadenosine 5'-diphosphate, an ecto5'-nucleotidase inhibitor, 30 min before electroacupuncture. The adenosine content of the spinal cord was detected using high-performance liquid chromatography. Lastly, the adenosine A1 receptor agonist N6-cyclopentyladenosine was intrathecally injected into the lumbar swelling of the rats, and the mechanical withdrawal and thermal pain thresholds were reevaluated. Results: Analgesia and increased ecto5'-nucleotidase expression and adenosine content in the spinal cord were observed 1 h after electroacupuncture. a,f3-methyleneadenosine 5'-diphosphate was able to inhibit upregulation of adenosine content and electroacupuncture-induced analgesia. After administration of N 6-cyclopentyladenosine, electroacupuncture-induced analgesia was restored. Conclusions:Our results suggest that electroacupuncture at Zusanli can produce analgesia in chronic constriction injury rat models, possibly via the increased ecto-5'-nucleotidase expression induced through electroacupuncture, thus leading to increased adenosine expression in the spinal cord.