A. Introduction

Acupuncture is a medical technique that has been practiced for over 3000 years in China, and is part of traditional Chinese medicine (TCM) and traditional Chinese veterinary medicine (TCVM). The use of acupuncture is becoming more common in veterinary medicine, and it can play a role in the management of acute, inflammatory, chronic pain, nerve damage, and nausea, and vomiting, as well as many other internal medicine problems.

In 1997, the United States National Institutes of Health (NIH) developed a consensus statement about acupuncture and its efficacy. NIH said that there was compelling evidence that acupuncture was useful in the management of osteoarthritis and musculoskeletal pain. It can be helpful in treating many gastrointestinal problems, including inflammatory bowel disease, diarrhea, ulcerative colitis, peptic ulcers, dyspepsia, abdominal pain, nausea, and vomiting. Acupuncture can help with management of pulmonary disease including colds and asthma. The immunomodulation of acupuncture can reduce inflammation, elevate WBC, and increase interleukin-2 production. Finally, acupuncture can help in treating reproductive disorders, decreasing uterine bleeding and regulating ovulation. In additions, the World Health Organization (WHO) also recognizes the use of acupuncture in the treatment of a wide range of common illnesses. While most of these studies reviewed the effectiveness of acupuncture in human patients, much of the data was based upon animal experimentation. Moreover, the conditions for which NIH and WHO thinks acupuncture can be effective are the same conditions which veterinarians treat with acupuncture.

From a modern prospective, acupuncture represents a form of nerve stimulation and neuromodulation of the body. As such, to know acupuncture is to know the nervous system. Certainly, we know that for acupuncture to work, it requires an intact nervous system and acupuncture is not effective if the nervous system is damaged beyond repair. Recently, using functional MRI (fMRI), the basic tenets of acupuncture have been proven. Those are that acupuncture is based upon the point selected, the method of stimulation and the duration of stimulation. Stimulation of various acupuncture points result is specific special changes in the central nervous system (CNS). The change is mild when only acupuncture needles are used and become more pronounced if electrical acupuncture is added. While the change initially is more limited, over time, the entire neural axis becomes involved.

B. Acupuncture

Acupuncture may be defined as the stimulation of a specific point on the body, referred to as an “acupoint.” Physiological changes in response to acupuncture point stimulation is the basis of clinical treatment. Some of these changes include release of endogenous opioids, immune system stimulation, and blood pressure regulation. Stimulation of an acupoint causes activation of Aα and Aβ nerve fibers to conduct electrical signals through the spinothalamic tract to the hypothalamus and cause release of β-endorphins. Acupuncture also causes activation of the descending pain inhibitory pathway which activates the periaqueductal gray matter to release more β-endorphins and the nucleus raphe magnus to release serotonins. Pain is blocked with the release of these endogenous opioids and neurotransmitters. Acupuncture can also activate T-cell lymphocytes and increase the number of white blood cells for the treatment of immuno-deficiency. Acupoint stimulation also affects the blood pressure receptors and can influence blood pressure. It can be used to increase or decrease blood pressure.

C. Acupuncture Points (Acupoints)

Most acupoints are located along the nervous system and have been identified to be one of four basic types of points (Gunn Cc. 1997):

1.  Type I acupoints, which make up 67% of all acupoints, are considered motor points. The motor point is the point in a muscle which, when electrical stimulation is applied, will produce a maximal contraction with minimal intensity of stimulation. Motor points are located in areas where nerves enter muscles. For instance, SI-9 is located at the junction of the deltoid muscle and triceps brachii and is supplied by axillary and radial nerves.

2.  Type II points are located on the superficial nerves in the sagittal plane on the dorsal and ventral midlines. For instance, Bai-hui lies in the depression between the spinous processes of the seventh lumbar and the first sacral vertebrae on the dorsal midline and is supplied by the dorsal branch of the last lumbar nerve.

3.  Type III points are located at high density loci of superficial nerves and nerve plexuses. For example, GB-34 is located at the point where the common peroneal nerve divides into the deep and superficial branches cranial and distal to the head of the fibula.

4.  Type IV points are located at the muscle-tendon junctions where the Golgi tendon organs are located. For example, BL-57 is located at the junction between the gastrocnemius muscle and the calcanean tendon.

The anatomic nature of acupuncture points represents neural vascular bundles, containing:

• Abundance of free nerve endings.
• Small arterioles, veins.
• Lymphatics.
• Increased concentration of mast cells.
• Contain higher conductance, lower impedance, and higher capacitance than adjacent tissues.
• Close proximity to somatic afferent terminals, suggesting the likelihood of interaction and modulation of afferent signals by needle placement.
• Most are also found in palpable depressions.

D. Pain Control Mechanism of Acupuncture

Many of the systematic reviews supporting acupuncture efficacy are for painful conditions. There are a few mechanisms by which acupuncture affects analgesia. These mechanisms have been extensively investigated and are quite well understood, and are enhanced with the passage of small amounts of electrical current through the acupuncture needle (electroacupuncture). These mechanisms are (Melzack R. 1965):

a. Local Effects

• A form of counter-irritation effect.
• Insertion of needle in an acupoint results in local tissue damage (called microtrauma), which activates Hageman’s tissue factor XII. This in turn results in the activation of local coagulation cascade and the complement cascade, leading to the production of plasminogen, protein kinins, and prostaglandins.
• The microtrauma also causes mast cell degranulation, which releases histamine, heparin, proteases, and bradykinin.
• These local reactions ultimately result in increased blood flow to the area and local immune responsiveness, that help relieve pain and reduce inflammation and edema.
• Connective tissues are stretched when needles are placed in acupoints rather, which relax the muscles and tissues in the local area.

b. Spinal Cord Effects

• When nerve impulses travel up the sensory nerves, it activates three centers (spinal cord, midbrain, and hypothalamus/pituitary) to produce analgesic effects.
• At the spinal site, enkephalin, and dynorphin are used to block incoming pain messages.
• Electroacupuncture at 2 Hz and 100 Hz cause the release of enkephalin and dynorphin in the spinal cord, respectively.

c. Brainstem Effects

• The neuronal network that serves acupuncture analgesia is thought to activate structures of the descending inhibitory pathways and deactivate limbic structures within the ascending nociceptive pathway.
• The midbrain uses endorphin to activate periaqueductal gray, and use serotonin and enkephalin to activate the raphe descending system, which then inhibit pain transmission within spinal cord.
• The pituitary releases beta-endorphin into the blood and cerebral spinal fluid to cause analgesia at a distance.
• The hypothalamus uses beta-endorphin to activate the descending analgesia system.

d. Gate Theory

• Acupuncture activates the Aβ fibers (larger and fast conducting nerve fibers than C fiber). These fibers lead to inhibition (pre-synaptic) of information carried by the C fibers (pain), so that the C fibers could no longer travel to the CNS to cause pain to the body.

e. Acupuncture on fMRI Function

• Acupoints that have analgesic properties associated with them tend to activate specific pain-associated brainstem regions. Non-analgesic acupuncture points do not activate these regions; rather they activate other regions of the brain (Chiu JH 2003).

f. Frequency of Electroacupuncture

• Low frequency (2–40 Hz) predominantly stimulates A-delta fibers and induces the release of beta-endorphin, met-enkephalin, and endomorphin from the brainstem predominately.
• High frequency (100 Hz) predominantly stimulates C fibers and selectively increases the release of dynorphin predominantly.
• Higher frequencies (200 Hz), predominantly stimulates serotonergic fibers and releases serotonin and epinephrine (Fwk S 1994).
• A combination of the two frequencies (2 and 100 Hz) produces a simultaneous release of all four opioid peptides, resulting in a maximal therapeutic effect. This finding has been verified in clinical studies in patients with various kinds of chronic pain including low back pain and diabetic neuropathic pain (Han JS 2004).
• One review showed that electroacupuncture activates the nervous system differently in health than in pain conditions, alleviates both sensory and affective inflammatory pain, and inhibits inflammatory and neuropathic pain more effectively at 2–10 Hz than at 100 Hz (Zhang R 2014).

Conclusion

In the past 30 years there has been increasing evidence to support the use of acupuncture as a therapeutic modality in veterinary medicine. There has been extensive research proving its analgesic effects, therefore, it is the primary clinical indication for its use in both human medicine and veterinary medicine.

Due to the intrinsic nature of the anatomical structures associated with the location of acupuncture points there are numerous systemic, local, and endocrine effects. For that reason, there are a variety of valuable clinical indications from pain management to cognition improvement and others. As more research develops in the upcoming years it is likely that acupuncture will become mainstream and a treatment modality taught in veterinary schools across the country.

References

1.  NIH Consensus Statement. Acupuncture. NIH Consensus Statement Online. 1997;15(5):1–34.

2.  World Health Organization. Acupuncture: Review and Analysis Reports on Controlled Clinical Trials. Geneva: World Health Organization. 2002. Internet resource.

3.  Chiu JH, Chung MS, Cheng HC, Yeh TC, Hsieh JC, Chang CY, Kuo WY, Cheng H, Ho LT. Different central manifestations in response to electroacupuncture at analgesic and nonanalgesic acupoints in rats: a manganese-enhanced functional magnetic resonance imaging study. Can J Vet Res. 2003;67(2):94–101.

4.  Fwk S. The neurophysiologic basis of acupuncture. In: Schoen AM, ed. Veterinary Acupuncture: Ancient Art to Modern Medicine, 1st ed. St. Louis, MO: Mosby; 1994:48,50.

5.  Gunn CC. Type IV acupuncture points. Am J Acupuncture. 1997;5:51–52.

6.  Han JS. Acupuncture and endorphins. Neurosci Lett. 2004;361(1–3):258–261.

7.  Hwang YC, Egerbacher M. Anatomy and classification of acupoints. In: Schoen AM, ed. Veterinary Acupuncture: Ancient Art to Modern Medicine, 2nd ed. St. Louis, MO: Mosby; 2001:19–21.

8.  Janssens L, Rogers P, Schoen A. Acupuncture analgesia: a review. Vet Rec. 1988;122:355–358.

9.  Leung MC, Yip KK, Ho YS, Siu FK, Li WC, Garner B. mechanisms underlying the effect of acupuncture on cognitive improvement: a systematic review of animal studies. J Neuroimmune Pharmacol. 2014;9:492–507.

10.  Melzack R, Wall PD. Pain mechanisms: a new theory. Science. 1965;150(699):971–979.

11.  Xie H. Xie’s Veterinary Acupuncture. Ames, IA: Blackwell Publishing; 2007:245–327.

12.  Zhang R, Lao L, Ren K, Berman BM. Mechanisms of acupuncture-electroacupuncture on persistent pain. Anesthesiology. 2014;120:482–503.