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Acupuncture Scientific Theories - Health Web |
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 Many hypotheses have been proposed to address the physiological mechanisms of action of acupuncture. To date, more than 10,000 scientific research studies have been published on acupuncture as cataloged by the National Library of Medicine database.
Neurohormonal theory
Pain transmission can also be modulated at many other levels in the brain along the pain pathways, including the periaqueductal gray, thalamus, and the feedback pathways from the cerebral cortex back to the thalamus. Pain blockade at these brain locations is often mediated by neurohormones, especially those that bind to the opioid receptors (pain-blockade site).
Some studies suggest that the Analgesic (pain-killing) action of acupuncture is associated with the release of natural endorphins in the brain. This effect can be inferred by blocking the action of endorphins (or morphine) using a drug called naloxone. When naloxone is administered to the patient, the analgesic effects of morphine can be reversed, causing the patient to feel pain again. When naloxone is administered to an acupunctured patient, the analgesic effect of acupuncture can also be reversed, causing the patient to report an increased level of pain. It should be noted, however, that studies using similar methodological procedures, including the administration of naloxone, have suggested a role of endogenous opioids in the placebo response, demonstrating that this response is not unique to acupuncture.
Such analgesic effect can also be shown to last more than an hour after acupuncture stimulation by recording the neural activity directly in the thalamus of the monkey's brain. Furthermore, there is a large overlap between the nervous system and acupuncture trigger points (points of maximum tenderness) in myofascial pain syndrome.
Evidence suggests that the sites of action of analgesia associated include the thalamus using fMRI (functional magnetic resonance imaging) and PET (positron emission tomography) brain imaging techniques, and via the feedback pathway from the cerebral cortex using electrophysiological recording of the nerve impulses of neurons directly in the cortex, which shows inhibitory action when acupuncture stimulus was applied. Similar effects have been observed in association with the placebo response. One study using fMRI found that placebo analgesia was associated with decreased activity in the thalamus, insula and anterior cingulate cortex.
Recently acupuncture has been shown to increase the nitric oxide levels in treated regions and resulting in increased local blood circulation, an outcome found in other studies. Effects on local inflammation and ischemia have also been previously reported.
Nerve-reflex theory
The nerve-reflex theory (developed by Ishikawa and Fujita et al. in the 1950s) proposed the reflex interactions between the periphery and the autonomic nervous system. This theory states that the skin (cutaneous) surface and internal organs (visceras) are intimately connected by these reflexes — "viscera-cutaneous reflex" and "cutaneous-viscera reflex."
These reflexes can be related to the neuroendocrine-autonomic responses, which is mediated partly by the hypothalamic-pituitary-adrenal axis (HPA axis). HPA axis is a complex set of feedback interactions between the hypothalamus (located in the midbrain), the pituitary (located beneath the brain) and the adrenal glands (located in the kidneys). The HPA axis is a major part of the neuroendocrine system that regulates stress responses and maintains the homeostatic condition of autonomic responses directly or indirectly, such as circulation regulation, breathing regulation, feeding behavior, weight control and digestion, immune responses, pain responses, acute stresses and chronic stresses, mood states, sexual/reproductive responses, growth, fluid balance and metabolic energy balances.
Recently, a broad sense hypothalamus-pituitary-adrenal (BS-HPA axis) model was proposed to explain the hypothesized analgesic effect of acupuncture based on observed neuroimaging (brain scanning) results using fMRI (functional resonance magnetic imaging) technique. The model incorporated the stress-induced HPA axis model together with neuro-immune interaction including the cholinergic anti-inflammatory model.
Gate-control theory of pain
The "gate control theory of pain" (developed by Ronald Melzack and Patrick Wall in 1962 and in 1965) proposed that pain perception is not simply a direct result of activating pain fibers, but modulated by interplay between excitation and inhibition of the pain pathways. According to the theory, the "gating of pain" is controlled by the inhibitory action on the pain pathways. That is, the perception of pain can be altered (gated on or off) by a number of means physiologically, psychologically and pharmacologically. The gate-control theory was developed in neuroscience independent of acupuncture, which later was proposed as a mechanism to account for the hypothesized analgesic action of acupuncture in the brainstem reticular formation by a German neuroscientist in 1976.
This leads to the theory of central control of pain gating, i.e., pain blockade at the brain (i.e., central to the brain rather than at the spinal cord or periphery) via the release of endogenous opioid (natural pain killers in the brain) neurohormones, such as endorphins and enkephalins (naturally occurring morphines).
Histological studies
In the 1960's, Bonghan Kim (medical scientist, North Korea) proposed that meridians and acupuncture points exist in the form of distinctive anatomical structures in his Bonghan Theory.
In the 2000's, some medical scientists started to take Bonghan Kim's theory seriously. Quite some papers were published by medical scientists in South Korea to follow up on Bonghan Kim's theory.
Issues in study design
One of the major challenges in acupuncture research is in the design of an appropriate placebo control group. In trials of new drugs, double blinding is the accepted standard, but since acupuncture is a procedure rather than a pill, it is difficult to design studies in which both the acupuncturist and patient are blinded as to the treatment being given. The same problem arises in double-blinding procedures used in biomedicine, including virtually all surgical procedures, dentistry, physical therapy, etc.
Blinding of the practitioner in acupuncture remains challenging. One proposed solution to blinding patients has been the development of "sham acupuncture", i.e., needling performed superficially a/o at non-acupuncture sites. Controversy remains over whether, and under what conditions, sham acupuncture may function as as true placebo, particularly in studies in pain in which insertion of needles anywhere near painful regions may elicit a beneficial response.
A study by Ted Kaptchuk et. al. showed that sham acupuncture exerted a stronger effect on pain than an inert pill did, and concluded: "Placebo effects seem to be malleable and depend on the behaviours embedded in medical rituals."
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