Neuropeptides SP and CGRP Underlie the Electrical Properties of Acupoints.
Kristen Sparrow • March 05, 2022
It’s hard to know if this is super relevant, but it caught my eye because of the new, pricey, monthly injectable for migraine that targets CGRP. Probably in no way pertinent, but I like to have this nonetheless. Another article on acupoints here.
| AMA | Fan Y, Kim DH, Ryu Y, et al. Neuropeptides SP and CGRP Underlie the Electrical Properties of Acupoints. Front Neurosci. 2018;12:907. Published 2018 Dec 12. doi:10.3389/fnins.2018.00907 |
|---|
Abstract
Electrical skin measurements at acupuncture points (acupoints) have been utilized as a diagnostic and therapeutic aid for more than 50 years. Although acupoints are described as having distinct electrical properties, such as high conductance and low impedance, the underlying mechanisms are currently unknown. The present study investigated in a rat model of hypertension whether the high conductance at acupoints is a result of the release of the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) during neurogenic inflammation in the referred pain area. When plasma extravasation from neurogenic inflammation was examined by exploring the leakage of intravenously injected Evans blue dye (EBD) to the skin, extravasated EBD was found most frequently in acupoints on the wrist. The increased conductance and temperature at these acupoints occurred during the development of hypertension. The increase in conductance and plasma extravasation at acupoints in hypertensive rats was ablated by cutting median and ulnar nerves, blocking small diameter afferent fibers with resiniferatoxin (RTX) injection into median and ulnar nerves, or antagonizing SP or CGRP receptors in acupoints. In turn, intradermal injection of SP or CGRP resulted in increased conductance and plasma extravasation in naïve rats. Elevated levels of SP and CGRP were found in the acupoints of hypertensive rats. These findings suggest that the high conductance at acupoints is due to vascular leakage following local release of SP and CGRP during neurogenic inflammation.
Significance Statement
Electrical skin measurements at acupuncture points have been utilized as a diagnostic and therapeutic aid for more than 50 years. Although acupoints are described as having distinct electrical properties, such as higher conductance and lower impedance than that of surrounding skin, the underlying mechanisms are completely unknown. Using a newly constructed electrode, intravenous injection of Evans blue dye, and cutaneous thermal recordings and imaging, the present study suggests a novel mechanism underlying the electrical properties of acupoints: the neuropeptides SP and CGRP produce high conductance at acupoints by causing neurogenic inflammation, plasma extravasation and accumulation of subskin water contents.
As the acupoints themselves are grossly anatomically invisible, several scientific approaches, such as electrodermal measurements (Ahn et al., 2008) and infrared thermal imaging (Yang et al., 2007), have been attempted to identify the acupoints. Notably, numerous studies have reported the electrical properties of acupoints. Since the 1950s, when Nakatani (1956) reported that there were some points on the skin with special electrical properties, experimental and clinical studies have been carried out in many countries including China, Japan, France, Germany, and the United States and suggest that acupoints have distinct electrical properties, including a higher conductance, lower impedance and resistance and increased capacitance compared to the surrounding skin (Ahn et al., 2008). As this view gained traction, many instruments such as acupoint detectors and electrodiagnostic devices have been developed and are increasingly used in acupuncture clinics. However, the mechanisms by which acupoints have these distinct electrical properties are currently unknown.
Our previous studies showed that in rat models of hypertension or colitis, the skin over acupoints exhibits neurogenic inflammation due to viscerosomatic convergence in sensory pathways (Kim et al., 2006, 2017). Neurogenic inflammation is characterized by vasodilation and vascular leakage (plasma extravasation) in the skin arising from the release of neuropeptides calcitonin gene-related peptide (CGRP) and substance P (SP) from activated small diameter sensory afferents (Schmelz and Petersen, 2001). The insights that many acupoints show neurogenic inflammation under certain conditions (Kim et al., 2006, 2017) and electrically high conductance/low impedance (Ahn et al., 2008; Colbert et al., 2008, 2009) have led to the hypothesis that the neuropeptides CGRP and SP evoke vascular dilation and leakage, causing the increased subskin tissue water content in acupoints and thus producing electrically high conductance and low impedance, potentially underlying the electrical properties of acupoints. To prove this hypothesis, the present study used a rat model of immobilization-induced hypertension (IMH) to investigate (1) whether acupoints exhibit active neurogenic inflammatory responses by using intravenous injection of Evans blue dye (EBD) and cutaneous thermal recordings and imaging and (2) whether acupoints have high conductance by using a newly constructed electrode and plasma extravasation. Furthermore, we explored (3) whether the increased conductance at acupoints is mediated by activation of small diameter afferents and generated by localized release of CGRP and SP.
