Participação das células gliais na hiperalgesia induzida pelo veneno de Bothrops jararaca e pelo conteúdo plaquetário: efeito da depleção de plaquetas circulantes

Abstract

Pain has a protective and adaptive role in the body, and is essential to alert about harmful stimuli in the environment. In this context, the increased response to painful stimuli is called hyperalgesia, in which astrocytes and microglia, presente in the spinal cord, act in the central mediation of this effect. Studies from our group demonstrated that platelets are involved in hyperalgesia induced by carrageenan and Bothrops jararaca venom (Bjv). Furthermore, it was observed that whole platelets or platelet releasate (PR) also induce hyperalgesia, suggesting that these cells play a crucial role in the genesis of inflammatory pain. Considering this information, the aim of this project is evaluate the participation of microglia and astrocytes, presente in the spinal cord, during the peak of hyperalgesia evoked by Bjv or by PR, as weel as the involvement of platelets in changes observed in glial cells. Hyperalgesia was assessed by analgesy-meter 2 hours after intraplantar (i.pl) injection of Bjv and PR, associated or not with different treatments, such as anti-rat platelet antibody (which causes depletion of circulating platelets) and minocycline (inhibit microglial activation). The results showed that both Bjv and PR induced hyperalgesia, wich was abolished by depletion of platelets, reinforcing the importance of these cells in the development of hyperalgesia. Microglial blockade also inhibited hyperalgesia induced by Bjv and PR. To confirm the involvement of glial cells, ipsilateral side of spinal cord samples of vBj and CSP, obtained from animals submitted to the nociceptive test, were quantified in western blotting (WB) analysis for microglia (Iba-1) and astrocyte (GFAP). The expression of Iba-1 and GFAP was up-regulated in both groups, Bjv and PR. However, platelet depletion only inhibited microglia marking in Bjv group, not interfering with the glial markers in the PR group, indicating that there is a relationship between circulating platelets and microglial activation during hyperalgesia evoked by Bjv. The role of NK1 receptors in hyperalgesia evoked by Bjv was also evaluated. The data obtained demonstrated that the NK1 receptor antagonist (GR 82334) inhibited the venom hyperalgesia. Furthermore, an increase in the expression of NK1 receptors was detected in the spinal cord of animals

injected with Bjv by WB, suggesting that NK1 receptors participate in the central mediation of this effect. Platelet depletion did not interfere with this effect. Taken together, these datas confirm the participation of circulating platelets in the genesis of hyperalgesia and demonstrate the involvement of microglial and astrocytic cells in the central mediation of hyperalgesia induced by Bjv and PR. Furthermore, the results suggest that the increase in microglial expression induced by Bjv is dependent on circulating platelets. In addition, suggest that the hyperalgesic effect of Bjv is mediated, at least in part, by NK1 receptors.