Activation of alpha7 acetylcholine receptors reduces neuropathic pain by decreasing dynorphin A release from microglia.

Dynorphin A is increased in neuropathic pain models. Activation of α7 n acetylcholine receptor (nAchR) reduces inflammation and pain. Whether activation of α7 nAchR affects dynorphin A release is unknown. The experiments evaluated the proinflammatory effect of dynorphin A in the spinal nerve ligation-induced neuropathic pain models and the effect of α7 nAchR activation on the dynorphin A content. α7 nAchR agonist, PHA-543613 and its antagonist, methyllycaconitine citrate were used and dynorphin A content was measured after spinal nerve ligation and in microglia cultures to test the analgesic mechanisms of α7 nAchR activation. The results showed that dynorphin A content peaked 3 to 7 days after nerve injury, and dynorphin A anti-serum intrathecal injection decreased IL-β and TNF-α content a week after nerve injury. Activation of α7 nAchR by PHA-543613 alleviated neuropathic pain behaviors and decreased dynorphin A concentration in the ipsilateral spinal cords. Also, PHA-543613 decreased dynorphin A release from the microglia cultures to LPS stimulation by activation of α7 nAchR. Our results suggest that dynorphin A contribute to the development and maintenance of neuropathic pain and that decreasing dynorphin A content by activation of α7 AchR of microglia is a potential therapeutic target for treating neuropathic pain.