Estudo do efeito analgésico do topiramato em modelos de dor aguda e neuropatia diabética

Abstract

In the present study, Topiramate (TP) was evaluated in acute pain and diabetic neuropathic animal models. Male Swiss mice were used in the tests of acute nocicepcion (formalin, hot plat and capsaicin) e male Wistar rats in the neuropathic pain test (filaments of von Frey). In the formalin test (2%, 20 µL/i.pl), it was measured the time spent by the animal licking the left hind paw which received the stimulation during 0-10 min (phase 01) and 20-40 min (phase 02).The results showed a reduction of the second phase (*** p<0.001) in the three doses used of TP while only the biggest dose showed effect in the first stage of test (*** p< 0.001). The TP effect (80 mg/Kg) was reverted by naloxone 2 mg/kg in the second phase of the test of the formalin, but not for glibenclamide 3 mg/kg, cyproeptadine 5 mg/kg and ondansetron 0.5 mg/kg when compared to control in both phases. In the hot plate test (52º) was analysed the reaction of the mouse to the thermal stimulation where the animal respond tryning to jump or to lick one of its brack legs. The animals had been submitted the plate to 00, 30, 60 and 120 min after the treatments and compared the groups that had received TP in the different doses (20,40 e 80 mg/kg). The results showed, TP demonstrated activity to 90 and 120 min (**p < 0.01; *** p < 0.001) only in the biggest dose used (80mg/kg). In another protocol, the animals received capsaicin (20 µL/2µg/i.pl), but the results ere not significant. For evaluations of the antinociceceptive action in neuropathic pain, the animals had been initially induced diabetes with streptozotocine 40 mg/Kg i.p. and after thirty days had been submitted to the test with filaments of von Frey. No significant effect of TP was observed in all doses used when compared with the controls. TP did not modify the frequency of locomotion of the animals in the open field and presented no effect in the Rota rod test suggesting that the TP does not exert its analgesic effect by depressive actions or relaxant muscular activity. In conclusion, the results may suggest that TP presents antinociceptive effect front the different stimulations of acute pain, but not in diabetic neuropathic pain. The analgesic effect in acute pain, probably involves system opioid, and seems do not involve potassium canals or serotoninergic system.