Scientific Basis of Acupunture Treatment

Antonio Alfaro Altamirano, DMV., MSc., Catedrático, Cert.Acup.
Phone 011 (506) 8381 1353, 8830 8362.
Telefax: 2203 5764. Costa Rica


Once the cause of bad performance has been identified objectively, at cervical, thoracic, lumbar, sacral or distal extremities, the diverse modalities of treatment in use today are anti inflammatory drugs injected directly into the supraspinal, interspinal or dorsal sacroiliac ligaments; ultrasound guided intraarticular injections of the dorsal articular processes intervertebral sinovial joints at cervical, thoracic or lumbar areas; ultrasound guided injections at lumbosacra and sacroiliac joints. Besides, the use of epidural steroids and other medications and diverse systemic treatments, modifying the athletic activity, specific exercises and physical therapy, segmental adjustments, are among the many therapeutic possibilities. Acupuncture, Mesotherapy and injections at “trigger points” complement the most popular and accepted variety of back treatments. Since little is known in our conventional approach about the complementary therapy and its bases of efficacy, re reviewed it here.


The objective in treating the muscular and skeletal lesions of the back is to get rid of pain, to restore the neuromuscular function and to regain mobility of spinal segments. The cause of pain and the vertebral segment involved must be identified to be able to eliminate the restriction. Thermography helps in identifying the area and segment involved and helps to objectively confirm the findings by palpation of the increase muscular tone, texture, and movement restriction. Thermography will show the asymmetric heat patterns as hot or cold spots; or concave or convex areas where they should be the oppossite.5, 13.

Receptors at joints and muscles (articular processes and Multifidus or paraspinal muscles) play an extremely important role in the perception of sensorial and motor pathways. The function of the propiocetive and nosciceptive receptors is the monitoring of tension of joint capsules, tendons and ligaments and their insertion at or close to joints and to offer an assessment of postural information and pain perception. Muscular and tendinomuscular receptors are located at paraspinal muscles and they register longitude and tension during contraction and relaxation16.

Abnormal conformation of extremities, back anatomy, type of training, training grounds, and postural position, they all generate imbalance in neuromuscular function. This unbalance state comes from a direct stimulus or trauma, exhaustion, radiculopathy or indirect effect from visceral problems, joint pain elsewhere or emotions. All of these are causes of referred pain due to multiple sensitive, motor and autonomic interconexions8. This pain is traditionally known as “Trigger points” and is located in areas of tendinomuscular junction or in the muscle mass or motor points9.

The change in the muscular function could produce permanent damage. These lesions will irritate the muscle, increase the muscle tone, and generate spasms. An animal working under these conditions generate cellular changes as lost of the cell membrane and longitude of fibers that will produce from functional restriction to structural restricton14. In this case, the pain is recognized as change in behavioral patterns or bad performance. This could generate a feedback pattern that could produce interneuronal sensitivity and be the origin of neuropathic pain. Neuropathic pain is referred to persistent pain arising from injuries to peripheral nerves, lynphonodes of the dorsal root, or the root itself or from central nervous system6.

Clinically we observe a patient with reflex induced hypersensitivity, to a point that he could react with aggressive behavior towards others. Puntiform digital palpation is all that is required with the aid of extension and flexion tests and thermography to identify the vertebral segment involved. Latter, Ultrasound, Radiology, Scintigraphy or Magnetic Resonance Imaging could be used.3, 4, and 16.


With the exception of neuropathic pain, every painful sensation has its origin at receptors on the periphery. These nosciceptors depolarize to thermal, mechanical or chemical stimulus. The nosciceptors are the not encapsulated terminal portion of afferent neurons of small diameter and not myelinized 12.

The peripheral nerve fibers can be divided in two categories: myelinized and not myelinized. There are 5 types of myelinized fibers: Aa , Ab , Ac, Ad and B.

The sensitive afferent fibers are nociceptive fibers. The nociceptive fibers are the myelinized Ad and the non myelinized C fibers. Fibers Aa, Ab, Ac and B are not nociceptive and they present bigger diameter and faster conductivity, they represent the tactile cutaneous receptors.12, 17.

The afferent nociceptive fibers present a grater threshold to stimulus and a slower conductivity. Fibers Ad respond with sharp, pricking pain while fibers C generate a deeper, burning sensation due to thermal, mechanical and chemical lesions and are called polimodal nosciceptors-C. Both fibers are located at deeper tissues such as viscera and joints.12, 17. Primary afferent neurons utilize excitatory neurotransmitters glutamate and aspartate at their termini and one or more of the neuropeptides substance P, calcitonin, and cholecystikinin as modulators and if sensitized, the nosciceptors respond to bradikinine, serotonin, histamine, potassium ion, acetylcholine and proteolytic enzymes. Prostaglandins and probably nitric oxide increase sensitivity. Ischemia is a well known cause of muscular pain and of spasm due to the production or cumulus of pro inflammatory substances that decrease pain threshold6.

The Spinocervicothalamic tract is primarily conductor of non noxious tactile information, and some information arriving from superficial structures as skin, witch is very well developed in the horse5 for example. Periphery myelinized bigger diameter neurons conduct non-nociceptive afferent signals to the epicritic system. This fine tactile conscious propiosception is felt at the sites known as Meissner, Ruffini, Pacini and Merkel,s Disc, and at free nerve end terminals. It is then conducted towards the nerve, ganglia, dorsal root and to the Medial Lemniscuses and from there to higher encephalic structures9. This stimulus activates cerebral conexions with central, autonomic, endocrine and immune repercussions toward maintaining homeostasis and thus restoring or healing1, 9. The anterolateral system carries sensations of somatic pain, temperature and tactile stimulus by the protopathic system, by the lateral pathway towards the Lemniscuses Lateral8. This system also conducts deep pain such as visceral and not cutaneous pain. Thru this way, the information arrives to cortex and thalamus for the conscious perception of pain1, 6, and 9.

Pain could be categorized as: Nociceptive: With an intact nervous system, the noxious stimulus generates a synaptic excitatory or inhibitory activity thru endogenous modulation of pain.
Neuropathic: Due to pathology somewhere in the nervous system that generates painful stimulus.
Idiopathic: When pain can not be explain in neuroanatomy or pathology12.

Endogenus inhibition of pain:

Among the central neural modulators we have the Mecencephalic Periaqueductal Grey (PAG), and the Nucleus Rafe Magnum (NRM), in the rostroventral medulla6. They represent the Pain Descendant Inhibition System from the brain to the spinal cord controlling the transmission of impulses from afferent nociceptive ways 6, 11. This analgesics system works thru the impulses that axons of the PAG send to the NRM, from where they descend thru the dorsolateral tract of the spinal cord to the inhibitory complexes at the dorsal horn. Here the pain could be blocked before it is perceived as such by the brain. The neurotransmitters involved are endorphinergic, adrenergic and serotoninergics. Endorphins, Encephalin and Dinorphins have a strong anti nociceptive action. The presynaptic inhibition over the Ad & C Fibers is due to the inhibition of Calcium channels at the membrane of sensitive nerve endings. This block lasts long periods. Endorphinergic cells also synapse with neurons from the spinothalamic tract. These cells are blocked by pos-synaptic inhibition. This is the way how pain is suppressed12.

Various stimuli could generate equilibrium between excitation and inhibition at the dorsal horn. Acupuncture, electroacupuncture, Mesotherapy and the injection directly on “Trigger points” are used due to their well known and documented analgesic action thru hyperstimulation3, 4, 7, and 10. This stimulus activates Aa and Ab type of fibers. Electroacupuncture generates low electrical stimulus and since must “trigger points” are indeed acupuncture points, and at the same time, these are motor points, these fibers are involved in the transmission of the low electrical stimulus or stimulus generated by similar means10, 17. This methods also stimulate Ad and C Fibers17. Nonetheless, the grater diameter fibers such as Aa and Ab are predominant during transmission of Acupuncture stimulus17. Identically, Mesotherapy stimulates fibers from the epicritic system that are located in the dermis and subcutaneous tissue generating an inhibition reaction4, 8. On the other hand, since “Trigger Points” are acupuncture points in 70% of cases, they could easily be located by electrodes passing a low intensity electrical flow. When the electrode is on top of the point, fasciculation or muscle contractions are obtained on top of the area. Once the trigger point is located injections of C fibers inhibiting compounds such as Sarraceniaceae to inhibit peripheral conductivity are used to obtain a relaxing effect (“The Gate Control Theory” by Melzac y Wall) 9, 10, 15.

Impulses generated by this means of complementary therapy, and conducted thru the major diameter afferent fibers, with no-nociceptive information about pressure, tactile and vibration stimulus, arrive at the Substancia gelatinosa, and synapse with neurons that “close the Gait” for the perception of pain, before pain conducted by less diameter nosciceptive fibers arrive. That inhibits the arrival at higher centers of conscious pain perception such as the Cortex and Hypothalamus. There is also interaction between noxious and not noxious stimuli at the spinal cord, such that local stimuli of Ad Fibers have the same effect 11, 16.

If there is articular pain, this is transmitted thru afferent nosciceptive Ad & C fibers. If at the same time we stimulate specific acupuncture points, or thru segmental mesotherapy, these stimulus will travel to the dorsal horn of the spinal cord thru Aa y Ab fibers which are of grater diameter, less threshold and then, faster conductivity. In this way more stimuli from acupuncture or mesotherapy arrive faster than painful ones inhibiting at presynaptic level its perception by neurotransmitters17. The principle of Transcutaneous Electrical Nerve Stimulation (TENS) is the same as in Acupuncture. It is the result of the interaction of complex opioides endogenous compounds with Substance P, Acetylcholine, Serotonin, Norepinephrine, and Gammaaminobutiric acid (GABA), for example. TENS and Acupuncture generate stimulus that alter spinal ways at segmental and super-segmental levels. Acupuncture is “super TENS” in a sense since in most patients it is easier to apply the electrodes at the needles rather than trying to fix the electrodes to different skin characteristics.

The segmental analgesia generated by Acupuncture, utilizes different compounds depending upon the stimulus employed. The use of filiform needles or electrical stimulation at low frequency such as 4-20 Hz generates central endorphin release into circulation and activates dinorphinergic neurons. Both, endorphins and dinorphins could be blocked by Naloxone (morphine antagonist). If we use frequencies from 80 to 100 Hz, the mediator will be Encephalin, and this compound can not be blocked by Naloxone. Higher frequencies such as 200 Hz will generate serotonin that could be blocked by serotonin antagonists. This could explain why some studies report different results2, 17. The results obtain thru Acupuncture will depend on the proper selection of points, the method of stimulation (electroacupuncture, acuapuncture, etc) and the intensity and duration of the stimulus. The use of functional Magnetic Resonance Imaging (fMRI) and Positron Emission Tomography (PET) has yielded enough scientific evidence of the special changes generated in the Central Nervous System. Changes are mild if only needles are employed but become more pronounced and longer lasting if electrostimulation is used2. The changes produced at cerebral areas well known for their analgesia effect are specific and well correlated to acupuncture points also known for their analgesia effect. The stimuli generated at points not related to acupuncture points do not produce this effects2. Thus fMRI and PET are two modern techniques that strongly support the use of this complementary therapy.

Viscera cutaneous reflexes:

To a visceral pain, there is a correspondent algid cutaneous spot or viscerotoma. This means that for example McBurney point is the viscerocutaneous reflex point for appendicitis and this point is no other than Stomach 30 in acupuncture terms.
In each of the segments of the posterior horn of the spinal cord there is a “pool” of afferent sensitive fibers from the skin and viscera. The visceral afferent fibers are non nosciceptive and they exert a helping action over the cutaneous afferent fibers which are also non nosciceptive. If there is a functional alteration on the viscera that is painful, these visceral impulses abnormal now, will bomb the secondary neurons at the level of the posterior horn of the spinal cord, decreasing their excitability threshold. These impulses are now sufficiently strong to overcome the synaptic barrier been received as algid sensations. The correspondent cutaneous are now sensitive, spontaneously, or due to pressure or palpation, what we in acupuncture call “Ah Shi Points” (“The pain is there”). These segmental relationships are used by the acupuncturist to transmit to the medullar vegetative zone impulses thru the placement of needles in such a way that the organism receives an information as to where to send a motor vegetative respond capable not only of controlling visceral pain as we described above but also to generate a vagosympathetic healing intervention that will modify its functional activity 8.


Acupuncture, Mesotherapy and Injection of “Trigger Points” induce segmental spinal inhibition of nosciceptive impulses generating immediate analgesia of variable duration and of local, segmental and central effects that produces relaxation and increase flexibility restoring neurotransmission and those segmental movements required for an optimal performance and wellbeing of our patients. Acupuncture, mesotherapy and the Injection of Trigger Points are considerate as Neuromodulation. They modulate receptors, effectors and peripheral nerve fibers with therapeutic purposes. They regulate the local, segmental and systemic nosciception. They not only control pain but they produce a positive effect in the increase of the immune response, homeostasis, activation of the peripheral nerve network and they are employed today not only for sedation and analgesia but also for Neuromodulation increasing performance, soundness and wellbeing8, 9 .


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11. -RIDGWAY, K.: Seminario-Taller sobre Terapia Alternativa en Equinos. 18 al 19 de junio, 2001 Escuela de Medicina Veterinaria. Universidad Nacional, Heredia, Costa Rica.

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13. TURNER, T.A.; PANSCH, J., and WILSON, J.H. Thermographic Assessment of Racing Thoroughbreds. In: The Elite Dressage and Three-Day-Event Horse. Conference on Equine Sports Medicine and Science 2002. Proceedings. P.p. 207-210. 18 al 23 de octubre de 2002. Saumur, Francia

14. -WALDSMITH, J. Thermography and Saddle Fit. Thermography, Advanced Workshop. 20 al 25 de Agosto del 2000. Newmarket, England.

15. -WALDSMITH, J. Finding and injecting “trigger points” on equine back problems. In: Equine Back and Pelvis Seminar. Virginia Equine Imaging Center. 29 y 30 de abril de 2002. Middleburg, Virginia, EUA.

16. -WOLF, L. The role of complementary techniques in managing musculoskeletal pain in performance horses. Vet. Clinics of North America: Equine Practice. Vol. 18 (1) 107-115, 2002. 17. -XIE, H.; OTT, E.A. and COLAHAN, P. Influence of acupuncture on experimental lameness in horses. In: 47th Annual AAEP Convention Proceedings. Vol. 47: 347-357, 2001.


Aa = A alfa
Ab= A beta
Ac= A gama
Ad= A delta