A series of tests involving humans, horses, and rodents has provided the most thorough picture yet of how electroacupuncture – a modern version of the ancient Chinese healing art – eases pain and promotes tissue repair.

The findings, by researchers at several institutions in the U.S. and South Korea, appeared online March 16 in the journal Stem Cells.

"We have discovered a mechanism which explains the benefits of electroacupuncture for treatment of injury–induced pain, and for tissue regeneration," said Dr. Fletcher A. White, one of more than 40 authors who contributed to the work. The key finding was that electroacupuncture triggers the release of mesenchymal stem cells (MSCs) into the bloodstream. These are adult stem cells found mainly in the bone marrow. The hardy cells, which multiply easily and turn into various tissue types in the body, are being widely studied for their healing potential.

The research was the culmination of efforts by four senior authors: Dr. Maria B. Grant, a professor of ophthalmology at Indiana University, began the work with Dr. Huisheng Xie, director of the Florida–based Chi Institute of Traditional Chinese Veterinary Medicine, in 2011 at the University of Florida. The work continued at Indiana University with the support of Dr. Mervin Yoder, director of the Herman B. Wells Center for Pediatric Research, and White, a neuroscientist at the Richard L. Roudebush VA Medical Center in Indianapolis, and a professor of anesthesia and pharmacology at Indiana University School of Medicine.

The study involved functional brain scans, blood tests, artery imaging, gene sequencing, and other lab methods. The researchers were able to trace electroacupuncture's actions on the brain and nervous system, resulting in the release of MSCs. The researchers believe the cells may be responsible for a range of therapeutic effects, such as the release of proteins that quell inflammation, and of the body's own natural opioids.

The main brain region affected was the hypothalamus, which controls the body's autonomic nervous system. This system works on an involuntary and reflexive basis, without our conscious thought, to regulate heart rate, blood pressure, digestion, and many other body functions.

In the study, functional MRI scans, which track blood flow in the brain, showed increased connectivity between the hypothalamus and the amygdala, the brain's emotion center. The study showed how stimulating the peripheral nervous system with needles leads to "rapid activation of the hypothalamus," according to White. This happened within 9 to 22 minutes, depending on the species. And then, within two hours, MSCs surged within the bloodstream.

Previous studies have suggested various theories for how acupuncture works, at least for pain. These have focused on the release of neurotransmitters, neuropeptides, and immune signaling proteins, or cytokines, in the central nervous system, and endogenous opioids into inflamed tissue.

The new findings don't necessarily contradict any of these theories, but add new insight, relating to the role of MSCs in the pain–relief process.

The downstream effects of MSCs are being studied further in the lab, says White. He believes they can be harnessed as a therapeutic tool in their own right.

To that end, a study is set to begin this spring at the University of Florida on using electroacupuncture–mobilized cells for treating acute tendon injuries in horses. The study will harvest the MSCs mobilized into the blood and expand them "ex vivo," or in culture in the lab. The aim is to get the cells to multiply without changing their properties. The researchers will then inject them back into the injured horses. The team hopes their findings will lead to FDA approval of the treatment for horses. Meanwhile, Grant and Yoder are pursuing the same approach in human studies.