Exploring the Science of Acupuncture (2024)

In a study published in 2020, Ma and his team discovered that this electroacupuncture effect was region specific: It was effective when given in the hindlimb region, but did not have an effect when administered in the abdominal region. The team hypothesized that there may be sensory neurons unique to the hindlimb region responsible for this difference in response.

In their new study, the researchers conducted a series of experiments in mice to investigate this hypothesis. First, they identified a small subset of sensory neurons marked by expression of the PROKR2^Cre receptor. They determined that these neurons were three to four times more numerous in the deep fascia tissue of the hindlimb than in the fascia of the abdomen.

Then the team created mice that were missing these sensory neurons. They found that electroacupuncture in the hindlimb did not activate the vagal-adrenal axis in these mice. In another experiment, the team used light-based stimulation to directly target these sensory neurons in the deep fascia of the hindlimb.

This stimulation activated the vagal-adrenal axis in a manner similar to electroacupuncture. “Basically, the activation of these neurons is both necessary and sufficient to activate this vagal-adrenal axis,” Ma said.

Neuroanatomic explanation

In a final experiment, the scientists explored the distribution of the neurons in the hindlimb. They discovered that there are considerably more neurons in the anterior muscles of the hindlimb than in the posterior muscles, resulting in a stronger response to electroacupuncture in the anterior region.

“Based on this nerve fiber distribution, we can almost precisely predict where electrical stimulation will be effective and where it will not be effective,” Ma explained.

Together, these results provide “the first concrete, neuroanatomic explanation for acupoint selectivity and specificity,” Ma added. “They tell us the acupuncture parameters, so where to go, how deep to go, how strong the intensity should be.”

He noted that while the study was done in mice, the basic organization of neurons is likely evolutionarily conserved across mammals, including humans.

However, an important next step will be clinical testing of electroacupuncture in humans with inflammation caused by real-world infections such as COVID-19. Ma is also interested in exploring other signaling pathways that could be stimulated by acupuncture to treat conditions that cause excessive inflammation.

“We have a lot of tough chronic diseases that still need better treatments,” he said, such as inflammatory bowel syndrome and arthritis. Another area of need, he added, is excessive immune reactions that can be a side effect of cancer immunotherapy.

Ma hopes that his research will ultimately advance scientific understanding of acupuncture and provide practical information that can be used to improve and refine the technique.

The work was primarily supported by the National Institutes of Health (grant R01AT010629), and partially supported by Harvard/MIT Joint Research Grants Program in Basic Neuroscience and the Wellcome Trust (grant 200183/Z/15/Z). For further information on salary support for the researchers, please refer to the paper.