Neurohormonal Explanantion of the action of acupuncture-induced analgesia

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 cortex back to the thalamus. Each of these brain structure processes different aspect of the pain — from experiencing emotional pain to the perception of what the pain feels like to the recognition of how harmful the pain is to localizing where the pain is coming from. Pain blockade at these brain locations are often mediated by neurohormones, especially those that bind to the opioid receptors (pain-blockade site). Pain relief by morphine drug (exogenous opioid) is acting on the same opioid receptor (where pain blockade occurs) as endorphins (endogenous opioids) that the brain produces and releases.

Some studies suggest that the Analgesic (pain-killing) action of acupuncture is mediated by stimulating the release of natural endorphins in the brain. This can be proven scientifically 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. This demonstrates that the site of action of acupuncture may be mediated through the natural release of endorphins by the brain, which can be reversed by naloxone.[9][10][11][12] Similar results were also obtained in experiments with animals showing that the analgesic effect is not due to subjective psychological placebo effect, but real physiological phenomena.[13] 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 (pain processing site) of the monkey's brain.[14] Furthermore, there is a large overlap between the nervous system and acupuncture trigger points (points of maximum tenderness in myofascial pain syndrome[15]).

The sites of action of acupuncture-induced analgesia are also confirmed to be mediated through the thalamus (where emotional pain/suffering is processed) using modern-day powerful non-invasive fMRI (functional magnetic resonance imaging)[16] and PET (positron emission tomography)[17] brain imaging techniques,[18] and via the feedback pathway from the cerebral cortex (where cognitive feedback signal to the thalamus distinguishing whether the pain is noxious (painful) or innocuous (non-harmful)) using electrophysiological recording of the nerve impulses of neurons directly in the cortex, which shows inhibitory action when acupuncture stimulus was applied.[19]

[9] Pomeranz B, Chiu D. Naloxone blocks acupuncture analgesia and causes hyperalgesia: endorphin is implicated. Life Sci 1976;19:1757-1762.
[10] Mayer DJ, Price DD, Raffii A. Antagonism of acupuncture analgesia in man by the narcotic antagonist naloxone. Brain Res 1977;121:368-72.
[11] Eriksson SV, Lundeberg T, Lundeberg S. Interaction of diazepam and naloxone on acupuncture induced pain relief. Am J Chin Med. 1991;19:1-7.
[12] Bishop B.Pain: its physiology and rationale for management. Part III. Consequences of current concepts of pain mechanisms related to pain management. Phys Ther. 1980, 60:24-37.
[13] Takeshige C, Tanaka M, Sato T, Hishida F. Mechanism of individual variation in effectiveness of acupuncture analgesia based on animal experiment. Eur J Pain 1990;11:109-13.
[14] Sandrew BB, Yang RC Jr, Wang SC. Electro-acupuncture analgesia in monkeys: a behavioral and neurophysiological assessment. Arch Int Pharmacodyn Ther. 1978 231:274-84.
[15] Melzack R, Stillwell DM, Fox EJ. Trigger points and acupuncture points for pain: correlations and implications. Pain 1977;3:3-23.
[16] Li K, Shan B, Xu J, Liu H, Wang W, Zhi L, Li K, Yan B, Tang X. Changes in FMRI in the human brain related to different durations of manual acupuncture needling. J Altern Complement Med. 2006;12:615-23.

http://en.wikipedia.org/wiki/Acupuncture#Scientific_theories_and_mechanisms_of_action