The Role of Glia Underlying Acupuncture Analgesia in Animal Pain Models: A Systematic Review and Meta-Analysis

As a traditional Chinese therapy, acupuncture is proposed worldwide as a treatment for pain and other health problems, but findings on acupuncture analgesia have been inconsistent because of its variable modalities of therapeutic intervention.This study aimed to evaluate the existing animal studies for evidence on acupuncture and its effect on glia in association with a reduction in pain conditions.Literature searches were performed in four English- and Chinese-language databases (Web of Science, PubMed, EMBASE, and CNKI) on October 8, 2021. Included studies reported the pain outcome (e.g., paw withdrawal latency, paw withdrawal threshold) and glia outcome (e.g., glial marker GFPA, Iba1, and OX42) in pain-induced animals during acupuncture treatment.Fifty-two preclinical studies were included in the meta-analysis. A single acupuncture treatment in rodents had an analgesic effect, which was more effective in inflammatory pain than in neuropathic pain in the early phase of treatment. The analgesic efficacy became more curative after repeated acupuncture. Furthermore, acupuncture treatment could effectively inhibit the activity of astrocytes and microglia in both inflammatory pain and neuropathic pain in a time-course pattern.Acupuncture treatment improves analgesic effect in rodent pain conditions under the possible mechanism of glial inhibition. Therefore, these results provide an opportunity to evaluate the effectiveness of acupuncture analgesia and neuroinflammation in animal models to research further neurobiological mechanisms and to inform the design of future clinical trials.PROSPERO (ID: CRD42020196011).