Understandings of acupuncture application and mechanisms

Abstract

Acupuncture involves the stimulation of acupoints, which are located at specific sites of the human body, by insertion of fine metal needles, followed by manipulation. Acupuncture has been proven to be an effective treatment in pain relief. Available evidence showed that acupuncture alleviates acute pain in conditions such as postoperative pain, acute back pain, labour pain, primary dysmenorrhea, tension-type headaches and migraines. In addition, acupuncture relieves chronic pain, for example, low back pain (LBP), knee osteoarthritis (KOA), headache, shoulder pain, and neck pain. For other diseases like insomnia, drug addiction and stroke, more high-quality randomized control trials (RCTs) are needed to confirm the efficacy of acupuncture, although there are particular difficulties surrounding adequate blinding and control group designs. Recent biomedical technology unveils the mechanisms of acupuncture. Studies have found that adenosine triphosphate (ATP) and transient receptor potential vanilloid (TRPV) channels are involved in the stimulation of acupuncture at the acupoint area. In the central nervous system (CNS), neurotransmissions including opioids, serotonin, norepinephrine, orexin and endocannabinoid are modulated by acupuncture to induce analgesia. Moreover, acupuncture reduces cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2) levels on the peripheral level by acting on the hypothalamic-pituitary-adrenal (HPA) axis, mediating peripheral opioid release. Acupuncture helps to treat insomnia by inhibiting sympathetic activity and down-regulating the HPA axis. Additionally, acupuncture reduces the effects of positive and negative reinforcements by modulating dopamine release in the nucleus accumbens. Recently, i-needles have been developed to allow for the analysis of metagenomics, meta-transcriptomics, and host-microbiome relationships following acupuncture, while skin implantable microsensors or needle-shaped microsensors are feasible for monitoring real-time microenvironmental changes in acupoints and even target organs. These studies may further accelerate the understanding of acupuncture's action mechanism.

Keywords: Acupuncture; analgesia; neurotransmission; opioids; pain.

Figure 1

Possible neurophysiologic mechanisms underlying acupuncture analgesia. Abbreviations: Arc, arcuate nucleus; PAG, periaqueductal grey; NRM, nucleus raphe magnus; LC, locus coeruleus; ATP, adenosine triphosphate; TRPV1, transient receptor potential vanilloid 1; 5-HT, 5-hydroxytryptamine (serotonin); NE, norepinephrine; SDH, spinal cord dorsal horn; HPA axis, hypothalamic-pituitary adrenal; COX-2, cyclooxygenase-2; PGE2, prostaglandin E2; MA, manual acupuncture; EA, electroacupuncture; RCTs, randomized controlled trials. The solid line indicates the pathway that has been shown in many studies, while the dotted line represents the pathway yet to be determined.