Physiology of Acupuncture: Review of Thirty Years of Research

Abstract: Acupuncture and electroacupuncture effects are mediated through a variety of neural and neurochemical mechanisms. Research done in the early 1970s first elucidated the mechanisms for the effect of acupuncture anesthesia. Further experiments showed that this effect can be transferred from one rabbit to another by cerebrospinal fluid (CSF) Transfusion. Further investigation explored the role of classic central neurotransmitters in the mediation of acupuncture analgesia, including catecholamines and serotonin. The availability of rat models for electroacupuncture, using the tail flick latency as a bioassay, allowed further experiments to be done to explain the basis for the effects. Differential release of central nervous system (CNS) opioid peptides by electroacupuncture has been noted, with 2-Hz electroacupuncture triggering release of enkephalins and ß-endorphins, and 100-Hz stimulation selectively increased the release of dynorphin in the spinal cord. A combination of both frequencies allows synergistic interaction among the three endogenous opioid peptides and a powerful analgesic effect. In addition, multiple acupuncture treatments with the optimal time spacing may result in an accumulation of electroacupuncture effect. A bimodal distribution of analgesic effect can be noted if a large group of rats is given electroacupuncture ('low responders" and 'high responders"). The mechanism of low response is at least twofold: a low rate of release of opioid peptides in the CNS, and a high rate of release of CCK-8, which exerts potent anti-opioid effects. A newly discovered anti-opioid peptide is orphanin FQ, which has also been linked to negative feedback control of electroacupuncture stimulation. Further research will serve to elucidate the mechanisms of acupuncture treatment in opiate detoxification, and how different disease entities may respond differently to electroacupuncture.

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