The Past, Present, and Future of Meridian System Research

In 1996, the U.S. Food and Drug Administration reclassified acupuncture needles and substantially equivalent devices from class III (premarket approval, investigational use) to class II (special controls), which includes medical devices for general use such as scalpels and syringes [1]. Hundreds of randomized controlled trials on acupuncture have been published [2]. Positive results of acupuncture were demonstrated in a variety of conditions such as renal colic [3], migraine [4], osteoarthritis [5], Raynaud’s syndrome [6], stroke [7, 8], and low sperm quality [9]. A systematic review of the high quality randomized controlled trials for acupuncture antiemesis showed consistent positive results across different investigators, different groups of patients, and different forms of acupuncture point stimulation such as electroacupuncture, laser, acupressure, and manual acupuncture [10]. The success of acupuncture has sparked many studies on the nature of the meridian system - the foundation of traditional acupuncture theory. According to the Standard Acupuncture Nomenclature proposed by the World Health Organization (WHO) [11], there are about 400 acupuncture points and 20 meridians/vessels connecting most of the points. Since the 1950s, it has been discovered and confirmed by researchers in several countries with refined techniques [12] that most acupuncture points correspond to the high electric conductance points on the body surface [13–17] and vice versa [18]. The high skin conductance of the meridian system is further supported by the finding of a high density of gap junctions at the sites of acupuncture points [19–22]. Gap junctions are hexagonal protein complexes that form channels between adjacent cells. It is well-established in cell biology that gap junctions facilitate intercellular communication and increase electric conductivity. Acupuncture and meridian points have also been found to have higher temperature [23], metabolic rates, and carbon dioxide release [24].