Sciatic Nerve Ligation in Rodents: A Morphological and Behavioral Study to Evaluate the Efficacy of Morphine and Ketoprofen

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Background: Traumatic nerve injuries are associated with neuropathic pain, which is resistant to conventional analgesics. Often, opioids do not have a beneficial effect. Hence, the aim was to evaluate its effect in an animal model and compare it to a nonsteroidal anti-inflammatory drug. Among the different preclinical models for nerve damage, partial sciatic nerve ligation (PSNL) shows persistent levels of nociception without autotomy. In the present study, the ligated sciatic nerve was assessed for damage. Morphine and ketoprofen from two distinct classes of analgesics were evaluated for antinociception in these rats. Materials and Methods: Sprague-Dawley rats were divided into the sham surgery ( n = 6) and PSNL group ( n = 30) where about 1/3–1/2 of the sciatic nerve was ligated. Histological analysis was performed at the end of the study by light and electron microscopy. Nociception was assessed once every week for 3 weeks by von Frey filaments. Nociception was noted to be present throughout the study in the neuropathic group with maximum nociception at the end of the 2 nd week when morphine or ketoprofen or both morphine and ketoprofen were administered in separate groups of animals. Results: Considerable degeneration was observed in nerve fibers and surrounding myelin within the sciatic nerve in rats with PSNL. Furthermore, these showed decreased withdrawal threshold, which persisted till the end of the study. Morphine and morphine + ketoprofen produced significant antinociceptive effect, but not ketoprofen. Conclusion: Morphine likely produced antinociception by binding to μ-opioid receptors. Inhibition of prostaglandin synthesis is not enough to relieve neuropathic pain. The results may have clinical relevance.