BACKGROUND AND OBJECTIVES: Selective serotonin reuptake inhibitors, such as fluoxetine, have been suggested as alternative to tricyclic antidepressants to treat chronic pain, due to the lower incidence of side effects. This study aimed at observing the effects of serotonin on acute pain modulation, by the administration of fluoxetine through the formalin test in rats previously submitted to sciatic nerve constriction. METHOD: We used 24 male Wistar rats, with mean weight of 300 g and distributed in 5 groups: 1. Control untreated; 2. Sciatic nerve constriction; 3. Sciatic nerve constriction and treated with 5 mg.kg-1.day oral fluoxetine for 15 days; 4. Sciatic nerve constriction treated with 5 mg.kg-1 oral reserpine every 72 hours and with 5 mg.kg-1.day oral fluoxetine for 15 days; 5. Sciatic nerve constriction treated with 5 mg.kg-1 oral reserpine every 72 hours for 15 days. All animals were submitted to modified formalin test after treatment. RESULTS: Response in the phase I, intermediate and phase II formalin test was not changed by sciatic nerve constriction. Treatment with reserpine or fluoxetine has not interfered with first and intermediate formalin test phases in the groups submitted to sciatic nerve constriction. The number of flinches in the second formalin test phase has increased in animals treated with fluoxetine and has decreased in animals treated with reserpine. There has been decrease in the number of flinches in animals treated with the association reserpina and fluoxetine as compared to animals treated with fluoxetine alone. CONCLUSION: Fluoxetine has increased painful sensation after acute stimulation in rats submitted to sciatic nerve constriction, showing the algogenic action of the drug in this experimental model.
Fluoxetine; Formalin test; Neuropathy; Pain; Reserpine
