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Biology 202, Spring 2005 Second Web Papers On Serendip

Acupuncture; A Frontier for Investigating Neurobiology and the Interconnectedness of Body Systems

Kate Matney

An indefinite understanding of how acupuncture works has largely excluded it from mainstream medicine and, more concretely, health insurance coverage. And yet, despite uncertainties surrounding acupuncture's mechanisms, its robust effectiveness has spurred its Western popularity. More and more practitioners and patient are seeking out the benefits of acupuncture. Reservations that it is merely a placebo-driven trend belonging to a new-age-sub-culture are challenged by its employment for animals. In fact, acupuncture for animals is very common in the most competitive arena for animal owners, horse racing (8.) There are many explanations for the mechanisms behind acupuncture's benefits ranging from the traditional discussion of Qi energy to physiological and biochemical understandings of its effects in the nervous system. With regard to its analgesic effects, advancements in neurobiology have humbled Western attitudes that acupuncture works by placebo. However, there are less clear understandings on how acupuncture treats ailments involving more systems than the nervous system and more symptoms than pain. Thus, acupuncture may serve as a jumping board for better investigating how the nervous system interacts with other systems.

Let us first survey the traditional practice and understanding of acupuncture. Procedurally, acupuncture is the scraping and puncturing of specific points believed to constitute the body's energy network, the Meridian system (6.) A large majority of points in the Meridian system target connective tissue planes, a continuous network enveloping all limb muscles, bones and tendons, surrounding all nerves and blood-vessels, and inserting every organ (3.) The predominance of connective tissue stimulation elucidates the integrative system through which acupuncture works and implies anatomical confirmation for its effects throughout the body. However, if acupuncture is just about stimulating the connective tissue to somehow affect its associated systems, why is it necessary to needle precise points? That is, why is needling not equally effective throughout connective tissue?

In fact, needling at precise Meridian points is shown to produce better results than "sham" acupuncture, which needles at non-acupuncture points. Penetration at sham points tends to share effects with Meridian penetration, but to a lesser degree. For example, a study on acupuncture in treating lower back pain caused by degenerative disk disease found acupuncture more effective than sham-acupuncture in reducing pain (1.) Meridian points might be more powerful penetration points because of two factors: the tissue's ability to create resistance with the needle, and the acupoint's proximity to nerve bundles.

A study comparing acupoints to sham points found that needle grasp of the tissue, measured by the resistance in removing the needle from tissue, was 18% greater in Meridian points (3.) The points' high resistance therefore results in a greater perturbation, which in turn produces an augmented mechanical stimulus. To effect nociception this mechanical stimulation must become sensory nerve input thereby translating into neuron signals. This translation from mechanical perturbation to neuron signaling indicates why acupoints are areas of high electrical conductance.

Experimental support for the higher sensitivity of Meridian points rests in their proximity to sensory nerve endings (10.) Researchers have shown that the nervous system and its signalers (neurotransmitters and endogenous substances) respond to needle stimulation and that a collection of nervous system afferent pathways (including anterolateral tract in the spinal cord, the raphne magnus and the dorsal part of the periaqueductal central gray) are affected by needling (4.) Of the 309 Meridian points traditionally used, 152 of them are directly over nerves, while 73 are within 0.5 cm of a nerve (11.) The precise combination of maximized tissue resistance and nerve proximity gives clues as to why puncturing Meridian points greatly accentuates effects more weakly displayed in sham acupuncture.

Meridian points' nearness to nerve endings fits with a principal hypothesis known as the "gate theory," which proposes that needling stimulates sensory nerves to the point of accommodation (10.) Accommodation essentially means that the strong continuous stimulation of needles activate nociceptors so much that the nerve sensitivity re-establishes equilibrium at a higher threshold, causing a desensitization of nerves. Accommodation of an inflamed or pained area could thus reduce or obliterate pain.

Studies started in the late 1970's provide more neuro-chemically based understandings of acupuncture's pain-reducing mechanisms. In 1977 experiments on rats found that the opioid antagonist naloxone, when microinjected into the periaqueductal gray matter and the hypothalamus, blocks the analgesic affect of acupuncture (4.) This not only demonstrated precise neurological sites of acupuncture analgesia, but also precise biochemical mechanisms involved in acupuncture. In addition to nerve accommodation then, acupuncture could be analgesic by stimulating the release of opioid peptides. Opioid peptides perform their analgesic effects by occupation and in turn, inhibition of sensory receptors whose excitation stimulates the release of proinflammatory neuropeptides. This argument was bolstered when research done a decade later showed that opioid peptides have peripheral as well as central nervous system receptors (7.) Like the gate theory, this evidence explained how acupuncture can have effects acting through afferent pathways to the central nervous system.

Perhaps the most interesting revelation in acupuncture analgesia is recent evidence for its upregulation of nitrous oxide (NO.) What was once considered only harmful (2) is now known to have wide ranging physiological functions including blood vessel dilation. Because of this effect NO is found in heart disease medication, as well as the popular impotence drug, Viagra (13.) A 2002 study on rats showed that hindlimb acupoints needling increases nervous system NO by upregulation of its protein synthesizer, neuronal nitric oxide synthase (nNOS.) NO upregulation is found in the gracile nucleus, an area of the brain which receives somatosensory nociceptive afferents from peripheral tissue where needling is executed (4.)

By providing improved scientific tools and models, such as the expanded role of NO, advancements in neurobiology have generated a greater acceptance for acupuncture as an analgesic therapy. However, there is much experimental evidence that beyond analgesia, acupuncture can treat a vast array of ailments. One interesting example is amenorrhoea, or menstruation loss, generally associated with an imbalance of hormones (8.) Preliminary studies show that acupuncture might in fact be more effective in treating amenorrhoea than hormone supplementation (14.) Because of its involvement with the endocrine system, amenorrhoea's response to acupuncture drives questions of how the endocrine and nervous system work together. Research on acupuncture is beginning to answer such questions and pose fare more. For this reason the cutting edge for acupuncture could also be a vanguard for neurophysiology. By understanding how acupuncture monopolizes on the interconnectedness of our bodies (as it must in treating amenorrhoea) acupuncture can guide the investigation of how body systems work together.


1) Goname EA, Craig WF, Whtie PF, et al. Percutaneous electrical nerve stimulation for low back pain: a randomized crossover study. JAMA 1999;281:818-823. (

2) Kibiuk, Lydia. "Nitric Oxide and Brain Damage" Brain Briefings 1999. (

3) Langevin, Helene M., Jason A. Yandow. "Relationship of Acupuncture Points and Meridians to Connective Tissue Planes" The Anatomical Record 269:257-265,2002. (

4) Ma, Sheng-Xing. "Neurobiology of Acupuncture: Toward CAM" Oxford University Press February 2004; 1(1)41-47. (

5) Middlekauff, Holly R., Jun Liang Yu, Kakit Hui. "Acupuncture effects on reflex to mental stress in humans" The American Journal of Physiology- Regulatory and Comparative Physiology 280:1462-1468, 2001. (

6) Shang, Charles. "The Meridian System and the Mechanism of Acupuncture" 1996. ( 7) Stein, Christoph. "Update on Peripheral Opioid Analgesia" European Society of Anesthesiology homepage (

8) The American Academy of Acupuncture and Oriental Medicine homepage; amenorrhoea

9) The American Academy of Veterinary Acupuncture's web site

10)Holistic Online.comó Acupuncture

11)Medical Pain Education homepage; "Channels and Acupoints: An overview."

12) The Skeptics Dictionary; Acupuncture.

13)Society of Neuroscience web page; Brain Briefing; Nitric Oxide and Brain Damage.

14)True Star Health Encyclopedia web page; amenorrhoea.

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