Scientists have performed acupuncture on mice with sore paws to pinpoint how the ancient Chinese medical practice might alleviate pain in humans.
After a half-hour session, the mice felt less discomfort in their paws because the needles triggered the release of a natural painkiller, say the researchers. The needles stimulated cells to produce adenosine, an anti-inflammatory and painkilling chemical, that was effective for up to an hour after the therapy was over.
The discovery challenges a widely held view among scientists that any benefit patients feel after having acupuncture is purely due to the placebo effect.
"The view that acupuncture does not have much benefit beyond the placebo effect has really hampered research into the technique," said Maiken Nedergaard, a neuroscientist at the University of Rochester Medical Centre in New York, who led the study.
"Some people think any work in this area is junk research, but I think that's wrong. I was really surprised at the arrogance of some of my colleagues. We can benefit from what has been learned over many thousands of years," Nedergaard told the Guardian.
Acupuncture was developed in China around 4,000 years ago. The procedure involves inserting fine needles at specific points around the body and then heating, twisting or even electrifying them.
Traditional practitioners claim acupuncture works by improving the flow of "qi energy" along "meridians", but the latest research, published in Nature Neuroscience, points to a less mystical explanation.
"I believe we've found the main mechanism by which acupuncture relieves pain. Adenosine is a very potent anti-inflammatory compound and most chronic pain is caused by inflammation," Nedergaard said.
The scientists gave each mouse a sore paw by injecting it with an inflammatory chemical. Half of the mice lacked a gene that is needed to make adenosine receptors, which are dotted along major nerves.
The therapy session involved inserting a fine needle into an acupuncture point in the knee above the sore foot. In keeping with traditional practice, the needles were rotated periodically throughout the half-hour session.
To measure how effective the acupuncture was, the researchers recorded how quickly each mouse pulled its sore paw away from a small bristly brush. The more pain the mice were in, the faster they pulled away.
Writing in the journal, Nedergaard's team describe how acupuncture reduced pain by two thirds in normal mice, but had no effect on the discomfort of mice that lacked the adenosine receptor gene. Without adenosine receptors, the chemical will have no effect on the mice when it is released in their bodies.
The acupunture had no effect at all in either group if the needles were not rotated.
Nedergaard said that twisting the needles seems to cause enough damage to make cells release adenosine. The chemical is then picked up by adenosine receptors on nearby nerves, which react by damping down pain. Further tests on the mice revealed that levels of adenosine surged 24-fold in the tissues around the acupuncture needles during and immediately after each session.
One of the long-standing mysteries surrounding acupuncture is why the technique only seems to alleviate pain if needles are inserted at specific points. Nedergaard believes that most of these points are along major nerve tracks, and as such are parts of the body that have plenty of adenosine receptors.
In a final experiment, Nedergaard's team injected mice with a cancer drug that made it harder to remove adenosine from their tissues. The drug, called deoxycoformycin, boosted the effects of acupuncture dramatically, more than tripling how long the pain relief lasted.
"There is an attitude among some researchers that studying alternative medicine is unfashionable," said Nedergaard. "Because it has not been understood completely, many people have remained sceptical."
Although the study explains how acupuncture can alleviate pain, it sheds no light on any of the other health benefits that some practitioners believe it can achieve.
