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

ABSTRACT 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 α,β-methyleneadenosine 5'-diphosphate, an ecto-5’-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 ecto-5’-nucleotidase expression and adenosine content in the spinal cord were observed 1 h after electroacupuncture. α,β-methyleneadenosine 5'-diphosphate was able to inhibit upregulation of adenosine content and electroacupuncture-induced analgesia. After administration of N6-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.

摘要 背景：针灸是神经病理性疼痛的治疗手段之一，但其作用机制尚未明确。既往研究发现，电针（Electroacupuncture, EA）干预后，神经病理性疼痛模型大鼠脊髓内腺苷含量升高可诱导镇痛效应，但电针引发该腺苷含量升高的具体机制仍未阐明。目的：本研究旨在明确胞外5'-核苷酸酶（ecto-5’-nucleotidase）在电针治疗神经病理性疼痛的镇痛效应中所发挥的作用。方法：我们在慢性缩窄损伤（chronic constriction injuries）诱导构建大鼠神经病理性疼痛模型后的第7天，于足三里穴实施电针干预。观察大鼠的机械撤足阈值与热痛阈值，并采用蛋白质印迹法（Western blot）检测脊髓组织中胞外5'-核苷酸酶的表达水平。在电针干预前30分钟，向慢性缩窄损伤模型大鼠腹腔注射胞外5'-核苷酸酶抑制剂α,β-亚甲基腺苷5'-二磷酸（α,β-methyleneadenosine 5'-diphosphate）；采用高效液相色谱法（high-performance liquid chromatography）检测脊髓组织的腺苷含量。此外，向大鼠腰骶部鞘内注射腺苷A1受体（adenosine A1 receptor）激动剂N6-环戊基腺苷（N6-cyclopentyladenosine），重新评估其机械撤足阈值与热痛阈值。结果：电针干预1小时后，大鼠脊髓内胞外5'-核苷酸酶表达水平、腺苷含量均升高，且出现镇痛效应。α,β-亚甲基腺苷5'-二磷酸可抑制电针诱导的腺苷含量上调与镇痛效应。给予N6-环戊基腺苷后，电针诱导的镇痛效应得以恢复。结论：本研究结果表明，足三里电针可在慢性缩窄损伤模型大鼠中产生镇痛效应，其潜在机制可能为电针诱导脊髓内胞外5'-核苷酸酶表达升高，进而促使脊髓腺苷含量增加。