Avaliação do efeito de substâncias analgésicas opioide, canabinoide, não esteroidal e estereoidal em larvas de Drosophila melanogaster no modelo de nocicepção térmica por radiação infravermelha

Abstract

Introduction: Currently, the use of animals in scientific research, mainly mammals, has been widely discussed. The attempt to reduce the number of animals used in the field of experimental nociceptive biology leads to development of new methods and introdution of new organisms models, such as Drosophilas. Scientific findings have demonstrated that class IV multidendritic neurons in third stage larvae Drosophila melanogaster are required in thermal nociception. In this way, the model organism was used to test substances and pro and antinociceptive procedures against infrared radiation. Objectives: To evaluate the effect of analgesic substances morphine, anandamide (AEA), dipyrone and dexamethasone in D. melanogaster larvae submitted to thermal stimulation by infrared radiation, and the effect of acetylsalicylic acid (AAS) and dexamethasone after sensitization by infrared light. Methods: Third stage larvae of D. melanogaster were immersed in 20 μL of water. Then, the drop was positioned perpendicular to infrared radiation (Hargreaves apparatus) with 95% maximum lamp intensity to evoke basal escape response, characterized by a roll of 360º on its own axis. The time interval between start of the stimulus and movement is called corkscrew latency, which is used as a measure of nociception. The substances under test were administered to larval hemocele in 0.1 μL diluted in artificial hemolymph using a micro-injection apparatus. For sensitization of nociceptors, each larva was stimulated for 32 s at 95, 97 or 99% intensities of the apparatus. The intensity of 97% was chosen for evaluation of the effect of AAS and dexamethasone. Results: To evaluate the antinociceptive profile of morphine, we measured the latency of corkscrew after 0, 5, 10, 15, 20, 30, 60 and 120 minutes (min) of morphine. It was observed a dose dependent effect (2, 4, 8, 16 ng) that reached the cutoff time (32 s) with the highest dose (16 ng). This maximal antinociceptive effect was completely reversed with concomitant administration of 4 ng of naloxone. Doses of 1 and 2 ng partially reversed the effect. It was used a similar protocol to investigate the antinociceptive effect of AEA. It was observed a dose-dependent antinociception (8, 16 e 32 pg). The maximum antinociceptive effect was achieved with 32 pg and it was not reversed with concomitant administration of 80 ng of CB1 receptor antagonist, AM251, or 100 ng of AM630, CB2 receptor antagonist. A dose-dependent antinociception was also observed after injection of dipyrone (32, 64 e 128 ng) and dexamethasone (4, 8 e 16 ng). When the thermal sensitization protocol was used, there was a reduction of the corkscrew latency, from 12 to 7,5 s. At basal level, larvae exhibited corkscrew when the temperature reached 30ºC and after sensitizationthey responded with 28.4ºC. We observed a dose-dependent antinociception of AAS (25, 50 e 100 ng) and dexamethasone (16 ng) after thermal sensitization. AAS had no effect on prior sensitization. It was also observed a long-term effect of dexamethasone (16 ng), which completely reverted thermal sensitization over 150 to 210 min, with peak action in 190 min. Conclusion: The results show that the modified model of nociception induced by thermal stimulation in D. melanogaster larvae was suitable for detection the antinociception actions of analgesics and nonsteroidal and steroidal anti-inflammatory drugs. Our findings open perspectives for the evaluation and discovery of antinociceptive drugs using a non-murine biological model. Financial Support: CNPq and CAPES.