Why acupuncture increases pain threshold of the rodent?
Scientists from the Laboratory of neuroreceptors and neuroregulators helped colleagues from Chengdu University (China) to conduct a series of in vivo experiments on wild-type and knockout by pain sensing receptors TRPV1 and P2X7 animals. It was shown that a stimulation of ST36 acupuncture point leads to an analgesic effect in the model of inflammation from the introduction of a slightly acidic solution into the paw, similar to the effects of selective TRPV1 and ASIC3 ion channel inhibitors. In the model of inflammation from the administration of α, β-meATP (a P2X1,3 purinergic receptor agonist) the ST36 point stimulation also reduced pain sensitivity, but not so effective as the P2X3 antagonist A-317491 or different ASIC3 channel blockers. The results are published in the British Journal of Pharmacology.
Traditional medicine of Southeast Asia region has in arsenal such treatments as acupuncture with special needles, or cautery using special wood sticks "Moxi" resulted in both cases in an effective pain relief through the skin of patients. This mechanical or thermal action is aimed in general to sensory neurons stimulating through the activation of a pool of receptors, which have become the object of this study. Wild-type rats and mice knocked out by TRPV1 or P2X7 receptors, both important for pain sensitivity, were used for experiments, and the pain relief was examined via acupuncture or moxibustion of point Zusanli ST36 on the left knee. The stimulation of the acupuncture point led to a stable analgesic effect in the model of inflammation from introduction of weakly acidic solution into the paw similar to the effect produced by selective TRPV1 and ASIC3 ion channel inhibitors. In the model of inflammation from the agonist of purinergic receptor P2X1,3 administration (α, β-meATP) stimulation of the ST36 point reduced pain sensitivity also, but was not such effective as an administration of the P2X3 antagonist A-317491 and ASIC3 channel blockers amyloride or sea anemone toxins APETx2 or Ugr9-1. The pain activation via another type of purinergic receptor P2X7 by a specific agonist have been effectively attenuated by acupuncture too. The injection of CFA into the animal’s paw known as standard method of inflammation modelling shown that both moxibustion and acupuncture were capable to reduce pain sensitivity with an effectivity like other tested inhibitors of receptors (ASIC3, P2X3, TRPV1, P2X7) but a longer analgesic effect was obtained by inhibitors combining: APETx2 (ASIC3) with A‐317491 (P2X3) only. As a result, it can be assumed that the analgesic effect of acupuncture and moxibustion can be reproduced by co-application of acid-sensitive and purinergic receptors inhibitors.