Somatosympathetic reflex and acupuncture-related analgesia.

Both acute and chronic pains correspond to nociceptive substances (NSs), which are naturally produced and metabolized by the organism experiencing the pains. The accumulation of NSs in regional tissues triggers a series of pathophysiological reactions and initiates certain threats to the health and the quality of human life. Pharmacological intervention is the most popular treatment for pain relief, which is achieved by either reducing the production of NSs or blocking the transmission of nociceptive signals through the nervous system, but no drug has been developed for the elimination of NSs. Therefore, improving blood circulation to eliminate NSs in painful tissues is an alternative strategy for pain relief. Acupuncture has been proved to be effective for the treatment of certain kinds of pain, but the mechanisms therein remain unclear. The effectiveness of acupuncture analgesia is also variable owing to the uncertainty surrounding the mechanism and the poor standardization of the technique. There is some evidence that acupuncture may induce pain relief by changing the regional blood flow through somatosympathetic reflex (SSR). Therefore, when exploring the mechanisms of SSR in detail, it is helpful to clarify the mechanisms of acupuncture analgesia and to develop a more standardized and effective protocol for acupuncture analgesia. Increasing evidence has suggested that both sympathetic activity and stimulation-induced SSR are differentially controlled in an organ-specific and activity-dependent manner. Vasomotor outflow, which involves the regulation of impaired regional blood circulation, is also differentially controlled in response to specific somatic stimulation. Therefore, we vigorously review the relations between SSR and acupuncture-related analgesia so that we can develop a targeted pain therapy where in certain areas of the body undergo site-specific somatic stimulation, which in turn, can adjust the impaired regional blood circulation.