Participação dos receptores de potencial transiente vanilóide do tipo 1 (TRPV1) no controle da dor neuropática

Abstract

Neuropathic pain can be caused by injury and dysfunctions in the somatosensory system. The transmission of nociceptive information occurs via the primary afferent fibers that initiate the transmission of pain information and expressing the transient receptor potential vanilloid 1 (TRPV1), a receptor involved in the transmission and modulation of pain signals and is a main stimulus transducer. Studies featured capsaicin in the effective treatment of neuropathic pain. Capsaicin causes a depletion of substance P by changing the transmission of pain, producing desensitization. The resiniferatoxin (RTX), a more potent TRPV1 agonist capsaicin that rapidly inhibit nociceptive transmission, provides lasting analgesia in behavioral models. These data support the development of new analgesics directed to neurons that express the TRPV1 receptor both central and peripherally. This study aims to evaluate the effect of RTX in hypernociceptive behavior of animals subjected to the model of neuropathic chronic constriction injury of the sciatic nerve (CCI). 112 males mice Swiss were used, (5-6 weeks, weighing 25 to 28g), subdivided into 2 groups: previous treatment group (pretreated with vehicle and false operated; pretreated with vehicle and neuropathic; pretreated with RTX and operated false and pre-treated with RTX and neuropathic) and late treatment group (false operated and treated with vehicle, false operated and treated with RTX, neuropathic and treated with vehicle and neuropathic and treated with RTX). RTX/vehicle was administered intrathecally, the mechanical nociceptive threshold was evaluated by Von Frey filament and Western blotting technique was used to evaluate the expression of TRPV1 receptors on dorsal root ganglia (DRG). The results found by nociceptive evaluation by Von Frey filaments demonstrate that the previous treatment group showed a significant increase of nociceptive threshold, demonstrating nociceptive effect of RTX for previous treatment after CCI and treatment group later neuropathic pain induced by CCI It was reversed after 1 hour of RTX administration and persist for up to 24 hours. In groups of neuropathic vehicle treated animals and the false-operated group treated with vehicle and RTX there was no difference between the times and change the nociceptive threshold. In the analysis of expression of TRPV1 it was observed that the expression of TRPV1 receptors significantly reduced the late treatment group compared to the vehicle group, and previous treatment, representing depletion of the TRPV1 receptors after intrathecal administration of RTX in animals subjected to CCI. It can be concluded that the TRVP1 receptors actively participate in controlling the neuropathic pain induced antinociception, as well as intrathecal administration of RTX 1 hour before to pain model showed that effect, however the expression of TRPV1 receptors were not changed.