SCIENTIFIC THEORIES AND MECHANISMS OF ACTION
The act of inserting a needle into an acupuncture point appears to be a simple procedure, however it stimulates a process that is very complex and the subject of most of the current research into how acupuncture works. There are currently four main theories(3), the gate theory, the neurohumeral hypothesis, the connective tissue theory and more recently the concept of limbic deactivation.
The gate control theory was developed in neuroscience independently of acupuncture. In this theory, pain is controlled by various inhibitory actions on the pain pathway by physiological, pharmacological and psychological means. It was later proposed as the possible mechanism as to how acupuncture modulates pain.
Inserting an acupuncture needle primarily stimulates the A delta and C fibres which transmit the signal via the spinal cord to the central nervous system, which then alters the processing and output. Acupuncture works by modulating the activity in the central, peripheral and autonomic nervous system.
The neurohumeral hypothesis suggests that the analgesic effect of acupuncture is associated with the release of endogenous endorphins in the brain. A large number of neurotransmitters act within this pain circuit and vary from changes in potassium and hydrogen ions, proteins (lymphokines), peptides (substance P, kinin, calcitonin, endorphins) and monoamines (glycine, noradrenaline, gamma amino butyric acid GABA). Generally these different groups of neurotransmitters occur peripherally and centrally. These effects can be reversed or blocked by naloxone.
It has been shown that needling an acupuncture point releases nitrous oxide and calcitonin gene related peptide, both strong vasodilators, which increase the nutritive blood flow and because of the effect on the arterio-venous shunt improve temperature control. The connective tissue releases nerve growth factor (NGF) stimulating nerve growth into the affected area and stimulating wound healing.
Viscero-somatic relationships have been described in animals as well as people. Dr.Oswald Kothbauer(4) in 1956 in a series of experiments to prove the relationship of the AEP’s and internal organs infused irritant solutions into the uterus and other abdominal organs of dairy cows. He found that points along the Bladder meridian were consistently painful, depending on which organ was infused and therefore these points could be used as diagnostic tools. His map of diagnostic points is widely used in cattle practice today, helping practitioners make a differential diagnosis of internal conditions in cattle.
A-delta fibres are found in viscera and have a similar distribution in the dorsal gray matter and tract of Lissauer in dorsolateral funiculus. Visceral and somatic sensory afferents can cause activation of each other, therefore somatic pain may cause visceral disease and visceral disease may cause referred somatic pain. Studies have shown that afferents from these points and organs overlap in the dorsal horn grey matter.
The visceral nociceptors terminate in the sympathetic chain and enter the spinal cord at T2 – L 2. (The Back Shu points of all the organs, apart from the small intestine and kidney are in this area). Bladder and genital receptors enter the spinal cord at S2 – S4. The Vagus nerve also contains a large portion of C fibres.
The Associated Effect Points (AEP’S) that lie lateral to the spine above the segmental nerves (on the Bladder meridian) seem the logical points that would affect organs. However other acupuncture points located on the limbs can also affect organ function. Some examples are:
– GV 26 on the philtrum of the nose that is used for shock and apnea. This point has been shown to increase adrenaline levels in the blood(5).
– PC 6 on the forearm that affects the heart. It slows the heart rate, increases the cardiac output and reduces arrhythmias.
– ST 36 on the lower leg that regulates acid secretion and motility of the stomach and digestive system and reduces hypertension.
The connective tissue theory was developed by Langevin(6) et al because in TCM the De Qi sensation is considered to be very important for a therapeutic response. The De Qi sensation has a sensory component that is felt by the patient as a sharp sensation, an ache or heaviness around the needle. It also has a biomechanical component, the “needle grasp” that is felt by the practitioner, making the needle difficult to remove. These researchers, through a number of experiments, concluded that during the De Qi sensation, the connective tissue and elastin fibres tightened around the needle, causing the needle grasp. The mechanical changes as the tissue fibres were stretched altered the intracellular actin polymerisation as well as the extracellular matrix. These changes were communicated from one cell to another sending a wave of connective tissue contraction and cell activation through the connective tissue. The researchers postulated that this may explain how the feeling of De Qi signal moves along an acupuncture meridian. By inserting acupuncture needles into cadavers and dissecting them to observe the position of the needles, Langevin(7) et al found that 80% of acupuncture points and 50% of meridian intersections on the arms coincided with intermuscular or intramuscular connective tissue planes.
The use of MRI’s to observe changes in the brain during acupuncture have added another dimension to acupuncture research. Changes have been shown to occur in the limbic system (amygdala and hippocampus), hypothalamus, sensory cortex and the frontal and prefrontal cortex. Overall acupuncture acts on the limbic system by activating pain inhibition, activating the inhibition of stress and decreasing brain activity while awake and asleep.
In a study by Hui(8) et al, these researches compared superficial needling with no De Qi and deep needling with De Qi with the following results:-
Subjects that experienced De Qi with soreness and numbness showed deactivation of the limbic system, particularly the amygdala and the hypothalamus, activation of the sensory cortex and no change in the frontal cortex.
Subjects that experience De Qi and pain from excessive stimulation showed an activation of the limbic system, sensory and frontal cortex.
Subjects that had “placebo acupuncture” i.e. superficial needling with no De Qi sensation showed a deactivation of the limbic system only.
Subjects receiving massage also showed a deactivation of the limbic system only.
The results of these MRI studies indicate that anything that touches the skin will affect the brain, but acupuncture affects different parts of the brain. Acupuncture induces the deactivation of the limbic regions and moderate activation of the somatosensory regions, which show virtual identity with the activation and deactivation networks of the resting brain.
In the normal brain there is a task negative network or default mode network (DMN) which is active during rest and deactivated when there are cognitive and conceptual tasks to be done. There is also a task positive network that is activated during active goal directed tasks. When one network is active the other is resting.
Hui et al hypothesised that acupuncture may mediate its diverse regulatory effects by promoting deactivation of the DMN and that additional limbic regions important to emotional processing may participate more often in acupuncture than in normal cognition and conventional sensory stimulation. Using MRI there was a close correlation to the appearance of the DMN at rest and in patients receiving acupuncture on the points studied. This seemed to correlate with the experience of De Qi.
The role of the DMN is to be prepared and alert and the integrity of this and the task positive network may be central to the balance of brain functions and maintenance of health. Its role in health and disease has recently become a subject of intense research interest. Its clinical relevance is indicated by the growing number of reports of its involvement in cognitive and behavioural disorders e.g. Alzheimer’s Disease, autism, schizophrenia, attention deficit hyperactivity disorder, Parkinson’s disease and Multiple Sclerosis. These studies have shown that alterations in the general activity and functional connectivity of the DMN in these patients.
SCIENTIFIC RESEARCH INTO ACUPUNCTURE EFFICACY
In the past 10 – 15 years there have been a large number of clinical trials as to the efficacy of acupuncture. Double blind trials are the accepted gold standard for drug trials, but since acupuncture is a procedure and not a pill, it is difficult to design studies where both the patient and the practitioner are blinded. In trying to quantify the placebo effect of acupuncture, researchers have used “sham acupuncture” where a needle is inserted into a non-acupuncture point usually several centimetres from the real acupuncture point on the assumption that it was an inert treatment. The results from many of these trials indicate that there was little difference in the clinical outcome between real and sham acupuncture although there is a difference in the effects in the brain (Hui et al).
The largest clinical study to date in people was done in Germany in 2007 with 454,920 treated by 8727 certified acupuncturists all with medical qualifications. The project was initiated by 10 private health funds and treatment was restricted to one of three conditions, low back pain 45%, headache 36% and osteoarthritis 12% (Other 7%). The aim of the study was to assess the effectiveness, safety and cost of acupuncture for these patients over a period of 2 years. The criteria for inclusion were that:-
– the disease had been present for at least 6 months
– the patient had been treated for the disease but not with acupuncture
– being insured
– the patient could stop treatment at any time, but the reason had to be documented
The results showed 22% had a marked improvement, 54% moderate improvement,16% minimal improvement, 4% poor. 8% patients reported mild side effects and 0.003% had severe side effects. The results confirmed that acupuncture in the hands of qualified therapists is safe. The demand for acupuncture was high and patients benefited from the treatment.
Another randomly controlled trial also treated these conditions and the results of the randomly controlled trial and the above clinical study are compared by Witt(10) et al. Their findings showed that acupuncture was more effective than conventional standard treatment (drugs), treatment without acupuncture or a waiting list control. A significant difference between acupuncture and sham acupuncture was only seen for arthritis of the knee, otherwise both showed similar effects, but both better than conventional therapy. Whether the effects of acupuncture are due primarily to specific or unspecific mechanisms appears to depend on the diagnosis and should be investigated in further studies.
The effects of acupuncture cannot be explained by a single mechanism. What starts as a local event spreads by way of the nervous system to affect most of the body. Ultimately the nervous system effects create changes in the endocrine system and the immune system. While the knowledge and theory behind the application of acupuncture in a clinical setting may be derived from antiquity, it has been modified and improved over the years. Much like modern Western medicine, acupuncture has evolved and its understanding developed with the passing years. Science is beginning to catch up and develop modern explanations for this ancient medical art. While there are likely to remain areas of traditional Chinese medicine appear to presently not have been proven scientifically, it may only be that we have not yet developed the means to evaluate them. Wisdom comes slowly in science.
Acupuncture has reached an all-time high for popularity and acceptance, but there is still a long way to go in defining how to integrate acupuncture with modern Western medicine. While they can exist together for the mutual benefit of the patient, some Western drugs can alter the responses to acupuncture and vice versa. Traditional Chinese medical theory and pattern recognition must evolve and be characterized in terms of Western medical theory so that a unified theory can evolve. At the same time, the individualized patient care provided by TCM approaches should be preserved as acupuncture becomes part of mainstream Western medical care.
Recognising our current limits to understanding how the central nervous system works is probably all that is required to realise why we do not fully understand acupuncture. Recent research advances in understanding brain function and the use of MRIs have also helped with understanding some of the acupuncture mechanisms. The discovery of mirror neurones which are scattered in pockets all over the brain that help us feel the pain and joy of others, the discovery that thoughts can alter the function of the brain, that one person’s thoughts can alter another’s, how things that you have learned to do changes the way your brain responds to a particular situation. If thoughts can alter brain function then the insertion of a needle may have an even more powerful effect on the brain and thereby cause healing and restoration of health.
Veterinarians who wish to practice acupuncture should undergo a training program. Currently the majority of certified veterinary acupuncturists in Australia and the Pacific Region have studied the International Veterinary Acupuncture Society’s basic acupuncture training program which requires a minimum of 150 hours of lectures and practical sessions plus assignments, case reports and a final theory and practical examination.
The Australian IVAS Veterinary Acupuncture Course is organised by the Australian Veterinary Acupuncture College Ltd. as Trustee for ACVA Foundation. This course which takes 18 months to complete, combines on line lectures with face to face workshops and as endorsed by the Australian Veterinary Acupuncture Group (AVAG).
Most veterinary acupuncturists integrate acupuncture into their daily practice, although there are some that use acupuncture alone or in combination with other complementary therapies.
1. Bensoussan Alan (1991) The Vital Meridian. Churchill Livingstone.
2. Gunn C.C. (1976) Acupuncture Loci – a proposal for their classification according to their relationship to known neural structures. Am J Clin Med 4:183-95.
3. Lundeberg Thomas (2010) Acupuncture a Western Perspective. 36th International Congress on Veterinary Acupuncture Aalborg. 37-44.
4. Kothbauer Oswald ( 1991), Veterinary Acupuncture for Cattle, Pigs and Horses. ZweimuhlenVerlag.
5. Still Jan (1991) Research in Veterinary Acupuncture. Belgium Veterinary Acupuncture Society.
6. Langevin H.M., Churchill D.L. and Cipolla M.J. (2001) Mechanical signalling through connective tissue:- a mechanism for the therapeutic effect of acupuncture. FASEB J. 15, 2275 -2282.
7. Langevin H.M., Churchill D.L.,Wu J., Badger G.J.,, Yandow J.A., Fox J.R., and Krag M.H.(2002) Evidence of Connective Tissue Involvement in Acupuncture FASEB J. 16 872 -874.
8. Hui KK, Liu J, Makris N, Gollub RL, Chen AJ, Moore CI, Kennedy DN, Rosen BR, Kwong KK. (2009) Acupuncture modulates the limbic system and subcortical gray structures of the human brain: evidence from fMRI studies in normal subjects. Hum Brain Mapp. (1):13-25.
9. Weidenhammer W., Streng A., Linde K., Hoppe A., Melchart D. (2007) Acupuncture for chronic within the research program of 10 German Health Insurance Funds – Basic results from an observational study. Complementary Therapies in Medicine (15) 238-246.
10. Witt C.M., Brinkhaus B., Willich S. N. (2006) Akupunktur Clinical Studies of benefits in patients with chronic pain.(article in German) Bundesgesundheitsbl-Gesunheitsforsch-Gesundheitzschutz. (49) 736-742.
Kendall, Donald E, (2002) Dao of Chinese Medicine – Understanding an Ancient Healing ArtOxford University Press.
Schoen, Allen M, (2001) Veterinary Acupuncture – Ancient Art to Modern Medicine, Moseby.
Xie Huisheng, Priest Vanessa (2007). Xie’s Veterinary Acupuncture, Blackwell Publishing.