Acupuncture can relieve many kinds of pain, but it remains unclear how it might work, beyond the possibility of a strong placebo effect. A study published online in Nature Neuroscience now shows that acupuncture locally activates pain-suppressing receptors which could be the key to the treatment's ability to relieve pain.
Maiken Nedergaard and colleagues inserted fine needles into the mouse equivalent of a traditional acupuncture point near the knee, and rotated these needles intermittently as is practiced by acupuncturists. This alleviated the pain reactions of mice with an inflamed paw, and it also strongly increased the local tissue concentration of the neurotransmitter adenosine. Pain relief required the presence of a particular adenosine receptor. It is known that this receptor resides on pain-transmitting nerve fibers and can reduce the activity of these fibers. The authors found that no pain relief or adenosine elevation was observed when the needles were simply inserted into the acupuncture point without rotation. They also noted that a drug that prolongs the lifetime of adenosine in live tissue helped to prolong the pain-attenuating effect of mouse acupuncture.
It should be noted that while this work suggests a mechanism for local pain relief by acupuncture, it does not in any way endorse the ancient mystical idea that the needles work by correcting some aberrant "qi" energy flow along "meridians". Instead, the authors propose a model whereby the minor tissue injury caused by rotated needles triggers adenosine release, which, if close enough to pain-transmitting nerves, can lead to the suppression of local pain.