Although acupuncture has long been used to treat pain, the underlying cellular and molecular mechanisms are not fully understood. The process appears to involve the brain's ability to produce opioids (pain-reducing chemicals) that bind to neurons in distinct regions of the brain, and the ability of neurons to produce receptors for these endogenous opioids—specifically, μ-opioid receptors (MORs). Recent clinical trials have indicated that both traditional (actual) and simulated (sham/placebo) acupuncture decrease pain, but other studies have suggested that the neural mechanisms involved may be different.
To investigate these neural mechanisms, NCCAM-funded researchers at the University of Michigan randomly assigned 20 women diagnosed with fibromyalgia (a chronic pain condition) to receive either traditional acupuncture or simulated acupuncture treatments in 9 sessions over 4 weeks. (In traditional acupuncture, needles are inserted at specific points on the body. Simulated acupuncture mimics this procedure, but without piercing the skin or using specific points. Participants did not know which treatment they were receiving.) At the initial session and again at the ninth, the women had positron emission tomography scans to analyze MOR binding potential in the brain, and they completed a questionnaire to assess pain intensity.
Traditional acupuncture increased MOR binding potential, in both the short term (right after the first treatment) and the long term (after 4 weeks), in several regions of the brain that process pain. Simulated acupuncture generally resulted in slight reductions in MOR-binding potential. Both traditional and simulated acupuncture groups experienced similar, significant reductions in clinical pain. In the traditional acupuncture group, greater long-term increases in MOR-binding potential were associated with greater reductions in pain.
The researchers concluded that, in fibromyalgia patients, different mechanisms appear to be involved in the analgesic effects of traditional acupuncture and simulated acupuncture. By increasing MOR-binding potential, traditional acupuncture appears to help the brain use endogenous opioids more effectively. The slight reduction in MOR-binding potential suggests that simulated acupuncture increases the brain's production of opioids. The researchers recommend additional studies to determine whether these differences are related to skin penetration of the acupuncture needles, point location, or both.
Harris RE, Zubieta J-K, Scott DJ, et al. Traditional Chinese acupuncture and placebo (sham) acupuncture are differentiated by their effects on μ-opioid receptors (MORs). NeuroImage.;47(3):1077–1085.2009