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Acupuncture (AP) is currently used worldwide to relieve pain. However, little is known about its mechanisms of action. We found that after spinal cord injury (SCI), AP inhibited the production of superoxide anion (O(2)·), which acted as a modulator for microglial activation, and the analgesic effect of AP was attributed to its anti-microglial activating action. Direct injection of a ROS scavenger inhibited SCI-induced NP. After contusion injury which induces the below-level neuropathic pain (NP), Shuigou and Yanglingquan acupoints were applied. AP relieved mechanical allodynia and thermal hyperalgesia, while vehicle and simulated AP did not. AP also decreased the proportion of activated microglia, and inhibited both p38MAPK and ERK activation in microglia at the L4-5. Also, the level of prostaglandin E(2) (PGE2), which is produced via ERK signaling and mediates the below-level pain through PGE2 receptor, was reduced by AP. Injection of p38MAPK or ERK inhibitors attenuated NP and decreased PGE2 production. Furthermore, ROS produced after injury-induced p38MAPK and ERK activation in microglia, and mediated mechanical allodynia and thermal hyperalgesia, which were inhibited by AP or a ROS scavenger. AP also inhibited the expression of inflammatory mediators. Therefore, our results suggest that the analgesic effect of AP may be partly mediated by inhibiting ROS-induced microglial activation and inflammatory responses after SCI and provide the possibility that AP can be used effectively as a non-pharmacological intervention for SCI-induced chronic NP in patients., (Copyright © 2012. Published by Elsevier Inc.)

Abstract: Here, we first demonstrated the neuroprotective effect of acupuncture after SCI. Acupuncture applied at two specific acupoints, Shuigou (GV26) and Yanglingquan (GB34) significantly alleviated apoptotic cell death of neurons and oligodendrocytes, thereby leading to improved functional recovery after SCI. Acupuncture also inhibited caspase-3 activation and reduced the size of lesion cavity and extent of loss of axons. We also found that the activation of both p38 mitogen-activated protein kinase and resident microglia after injury are significantly attenuated by acupuncture. In addition, acupuncture significantly reduced the expression or activation of pro-nerve growth factor, proinflammatory factors such as tumor necrosis factor-α, interleukin-1β, interleukin-6, nitric oxide synthase, cycloxygenase-2, and matrix metalloprotease-9 after SCI. Thus, our results suggest that the neuroprotection by acupuncture may be partly mediated via inhibition of inflammation and microglial activation after SCI and acupuncture can be used as a potential therapeutic tool for treating acute spinal injury in human. [Copyright &y& Elsevier]