Participação dos receptores de potencial transiente no efeito antinociceptivo da acupuntura nos modelos de dor fásica, inflamatória e neuropática

Abstract

Pain may be classified as inflammatory, neuropathic and phasic, which occurs by a damage in the nervous system and nociceptors stimulation, such as the Transient Receptor Potential (TRP’s). In TRP’s group, we highlight the TRPV1, TRPM8, and TRPA1, stimulated by substances anti-nociceptive, such as capsaicin, menthol, and methyl salicylate respectively. This work sought to investigate the role of the TRP’s on the antinociception, trough administration of agonists in the acupoint Zusanli (ST36), in inflammatory, neuropathic and phasic pain models. The project has composed by 180 male Wistars rats, 6 weeks old, between 250g to 300g. The inflammatory pain model induced by Complete Freund’s Adjuvant (CFA), phasic pain model by Tail Flick (TF) and neuropathic pain model by Chronic Constriction Injury (CCI). A subcutaneous injection in the acupoint Zusanli 20μL of saline and the TRP 's agonists, capsaicin , menthol and methyl salicylate was applied in doses of 0,03 μg/20μL; 0,3 μg/20μL; 3,0 μg/20μL. Mechanical thresholds assessed using a digital Von Frey device before the administration of CFA and after 0, 1, 3, 6 and 24 hours of administration of the agonists. The TF thresholds assessed before and after 0, 1, 3, 6 and 24 hours. Inflammatory hyperalgesia revealed significantly reversed in all agonists. The administration of capsaicin induced the reduction of hyperalgesic effects at all periods, in 3 doses, except for the time after 24 hours of treatment, where only the higher dose induced a reduction in a mechanical threshold. The treatment with menthol and methyl salicylate induced an antinociceptive effect in the acupoint for all the times, in different doses. In phasic pain group, the administration of agonists, capsaicin, and menthol increased the latency thresholds, at all times evaluated in three doses except the T0. In addition, the administration of methyl salicylate obtained an analgesic effect on all doses and on the times T3, T6 and T24, and only the highest dose had an effect on T0 and the intermediate dose on T1. In neuropathic model pain, capsaicin in the highest and intermediate dose showed analgesic effect in all the times. The mentol and the methyl salicylate had this effect in all the dose and the most times. According to the results obtained so far, we suggest that TRPV1, TRPM8, and TRPA1 receptors are involved in anti-hyperalgesic effect by administering agonists in the Zusanli acupoint in the control of inflammatory and phasic pain.