Early studies from several independent laboratories demonstrated that
acupoints possess the characteristics of low electrical resistance. New devices are developing to increase the reliability of electrical skin impedance measurements for counteracting the factors including skin dryness, skin thickness, size of the sensing
electrode, pressure applied on the
electrode, interelectrode distance, room temperature, and humidity. Morphological studies have identified that blood vessels, hair follicles, and nervous components are enhanced in the
meridians/
acupoints, which represent areas of potentially high neuronal activity. Recent evidence shows that
nitric oxide (NO) concentrations are enhanced in skin
acupoints/
meridians.
L-arginine-derived NO synthesis modifies skin
norepinephrine (NE) synthesis/release in
acupoints/
meridians, and NO-NE activations play an important role in mediating the skin conductance responses to electrical stimulation. NOergic signaling molecules interact with gap junction and transient receptor potential vanilloid type-1. Other studies reported that the high conductance at
acupoints is a result of the release of the
neuropeptides substance P and
calcitonin gene-related peptide during
neurogenic inflammation in the
referred pain area. Pathological body conditions caused considerable changes in skin conductance or impedance at
acupoints. Although systematic research with an improved equipment and research design to avoid the influencing factors are requested for a definite answer in this field, the results from anatomical and biochemical studies consistently show that
acupoints exist higher levels of nervous components, and NOergic signaling molecules and
neuropeptides involved in the skin low resistance at
acupoints. The increased interest in the
acupoints/
meridians has led to an open-minded attitude towards understanding this system, which is fundamental important to establish the valid aspects of scientific basis of Chinese medicine mechanisms and
therapies.