The Antinociceptive Effect And The Possible Mechanism Of Acupoint Stimulation With Chemical Irritants In The Bee Venom Pain Model

Objective:Bee venom(BV) can cause pain,but a lot of studies have demonstrated the antinociceptive and anti-inflammatory effect of the injection of bee venom (BV) into Zusanli (ZSL) acupoint in rats. The present study is designed to determine whether the injection of chemical irritants such as formalin and CFA, as well as BV, into ZSL acupoint can produce the the antinociceptive and anti-inflammatory effect in the bee venom model and the possible underlying mechanisms.Methods: We use BV-induced pain rat model to investigate the roles of ZSL BVA in the PSN, mechanical hyperalgesia and inflammation reaction of the injected hind paw. The experiments were performed on Sprague-Dawley albino male rats weighing from 250~300g.First, the effect of the injection of BV, formalin and CFA into ZSL acupoint on intraplantar BV-induced persistent spontaneous pain, mechanical hyperalgesia and inflammatory swelling of the injected paw was observed. Furthermore, the effect of pre-treatment with naloxone (5 mg/kg, i.p.) and the injection of 0.15% capsaicin into ZSL acupoint on the antinociceptive effect of BV acupuntrue (BVA) was observed.Results: The results showed that all treatment groups including BV, formalin, and CFA injections into the back, saline injection into ZSL, and BV injection into ZSL produced a significant inhibition of intraplantar BV-induced persistent spontaneous nociception (PSN) and mechanical hyperalgesia, but had no effect on intraplantar BV-induced inflammatory swelling. The results showed that pre-treatment with naloxone had no effect on BVA-induced antinociceptive effect on intraplantar BV-induced PSN and mechanical hyperalgesia, while pre-treatment with capsaicin produced a partial blockage on re-treatment with naloxone had no effect on BVA-induced antinociceptive effect on intraplantar BV-induced PSN and mechanical hyperalgesia intraplantar BV-induced PSN, but had no effect on BVA-induced anti-nociception of mechanical hyperalgesia.These results suggest that chemical irritants acupuncture produced the anti-nociceptive effect, but not anti-inflammatory effect in the bee venom pain model, and that chemical irritants acupunture-induced analgesia is a common mechanism, not specific for bee venom. Furthermore, the present results suggest that BVA-induced anti-nociceptive mechanism is partially mediated by capsaicin-sensitive primary afferent fibers, but not endogenous mu opioid receptors in the bee venom pain model.