Acupuncture and Serotonin

Acupuncture and Serotonin

Changzhen Gong, Ph.D.

Acupuncture, a medical modality of traditional Chinese medicine, has been practiced for several thousand years. It involves the insertion of thin needles into specific sites called acupuncture points which are distributed along vital energy pathways on the body known as meridians. Acupuncture is effectively applied to diseases ranging from chronic and acute pain conditions, internal disorders, and pediatric conditions to gynecological and neurological disorders. Since its introduction to the U.S. in the 1970s, acupuncture has achieved a prominent position among alternative and complementary medicine modalities. But how does acupuncture work? What is the mechanism behind acupuncture’s therapeutic function? Exploration of this question by the scientific research community has resulted in a number of studies suggesting that acupuncture can directly affect the production and release of a number of chemical substances in the body, including serotonin.

Serotonin, also called 5-hydroxytryptamine (5-HT), is a hormone which is found in the central nervous system, blood platelets, digestive tract, and pineal gland. A hormone is a chemical substance produced in one part of the body that regulates and controls the activity of tissues or organs in another part of the body. In the brain, serotonin acts as a classic neurotransmitter, mediating nerve impulses between cell synapses. As a component of blood platelets, serotonin acts as a vasoconstrictor, causing blood vessels to narrow. Approximately 80% of the body's total serotonin is in the intestinal tract, where it stimulates smooth muscle contractions. Serotonin is involved in many physiological functions including appetite, mood, hormonal balance, sleep cycles, alertness, inhibition of gastric secretions, stimulation of smooth muscles, and vasoconstriction. Changes in serotonin production are believed to be at least part of the clinical basis for depression, premenstrual syndrome, eating disorders, and a variety of other health problems. Low levels of serotonin in the brain have been correlated with clinical depression. Scientists have found that acupuncture can regulate the production and release of serotonin, based on analysis of serotonin levels in blood and spinal fluid.

Acupuncture Affects Neurotransmitters and Neuropeptides

A wide variety of scientific studies indicate that acupuncture increases the levels of a number of key chemical substances in the blood and cerebrospinal fluid. Besides serotonin, these include the neuropeptides endorphin and enkephalin, which are powerful analgesics, and the hormones epinephrine and norepinephrine, which regulate blood pressure, among other functions. Currently, this is considered to be the most important mechanism to explain how acupuncture works.

One way of measuring the effects of acupuncture is to analyze the levels of hormones and neurotransmitters in the blood and spinal fluid. In the last two decades, a new technology –functional magnetic resonance imaging (fMRI) – has enabled scientists to pinpoint the effects of acupuncture on specific areas of the brain. For example, it has been shown that a part of the brain – the medullary raphe nuclei – processes somatic signals during electroacupuncture and participates in acupuncture-related modulation of cardiovascular function through an opioid or serotonergic mechanism.

It is interesting to note that there are various subtypes of serotonin receptors on cells, and that these receptors can occur in different combinations in different individuals. This is also the case for other hormones and neurotransmitters. This may explain why people respond differently to acupuncture stimulation at an individual level.

Pain, Depression, and Addiction

In the West, acupuncture has been most widely accepted as a way to relieve pain and reduce stress. Serotonin, functioning as a neurotransmitter, is involved with both analgesia and mood perception. Some antidepressant medications affect the action of serotonin as a means to treat depression. One study of electroacupuncture analgesia found serotonin-releasing neurons and several subtypes of serotonin receptors affecting the descending pain inhibitory pathway in the lower brainstem. In a comparative neurotransmitter study on the analgesic mechanism of electroacupuncture, the analgesic effects of electroacupuncture were demonstrated to be related to opioid, adrenergic, serotonin and dopamine receptors in an arthritic pain model using rats. A depression study using rats as an animal model showed that acupuncture stimulation can relieve maternal separation-induced behavior changes in young rats.

Acupuncture has been used in the United States since the 1970s to treat substance addictions such as alcohol, drugs, or nicotine. A study to explain the effectiveness of acupuncture in the treatment of drug addiction indicated that acupuncture's role in suppressing the reinforcing effects of abused drugs takes place by modulating mesolimbic dopamine neurons. Several brain neurotransmitter systems, including serotonin, have been implicated in the modulation of dopamine release by acupuncture.  These studies provide evidence for the biological effects of acupuncture that ultimately may help us to understand how acupuncture can be used to treat drug addiction.

 

An expanded version of this article appears in the International Journal of Clinical Acupuncture, No. 4, 2013.