BACKGROUND AND OBJECTIVES: Different receptor systems are involved with central pain modulation: noradrenergic, serotoninergic and opioid among others. This study aimed at evaluating amitriptyline effects on pain modulation in rats submitted to sciatic nerve ligation. METHOD: The sample was made up of 24 male Wistar rats, mean weight of 300g, which were distributed in 5 groups: (C) control without treatment (n = 4), (LC) submitted to sciatic nerve ligation (n = 5), submitted to sciatic nerve ligation and treated with: (A) amitriptyline (n = 5), (R) reserpine (n = 5), (AR) reserpine + amitriptyline. All animals were submitted to modified formalin test. RESULTS: Sciatic nerve ligation has decreased nociceptive response. Reserpine administration has not interfered with pain response in formalin test phase 1. Amitriptyline has restored pain response in formalin test phase 1, indicating peripheral nociception potentiation, and has decreased the number of flinches during the intermediate formalin test phase, in the absence or presence of reserpine, indicating potentiation of pain response inhibitory descending way. Sciatic nerve ligation has decreased response in formalin test phase 2. Amitriptyline has restored previously observed response. CONCLUSION: Treatment with amitriptyline and reserpine allows suggesting that in the peripheral neural injury model, norepinephrine participates in the injuring signal transduction, in the pain inhibitory descending way modulation and in the inflammation-induced nociception. The participation of other inflammatory response mediators and of serotonin should be considered.
Amitriptyline; Formalin test; Neuropathy; Pain; Reserpine
