Fluoxetine, a selective serotonin reuptake inhibitor modulates inflammatory and neuropathic pain in the rat

The clinical usefulness of classical tricyclic antidepressants has been indicated in a variety of neuropathic pain. The role of selective serotonin reuptake inhibitors (SSRIs) is, however, controversial in pain control. The present study was aimed at evaluating the efficacy of an SSRI, fluoxetine, in neuropathic pain involving peripheral (carrageenan-induced inflammation) and central sensitization (spinal nerve ligation) in rats. Fluoxetine was also assessed for antinociceptive and antiphlogistic effect against acetic acid-induced chemonociception in mice and carrageenan-induced inflammation. Fluoxetine (100-400 μg, intraplantar administration) failed to attenuate either hyperalgesia or cold allodynia in any of the tests employed. Fluoxetine dose dependently increased paw volume in the absence or presence of an inflammatory stimulus which was not reversed by indomethacin (10 mg/kg, p.o). Fluoxetine was ineffective in reducing hyperalgesia and allodynia associated with the rat models. However, fluoxetine dose dependently decreased acetic acid-induced writhings. The results indicated that 5-HT plays a differential role in pain modulation and may not be playing a major role in the maintenance of hyperalgesia and allodynia in the rat models.