Opioids in neuropathic pain

Abstract

Neuropathic pain in human appears not to be opioid‐resistant but only reduced sensitivity to systemic opioids is observed in this condition. We studied the contribution of central and peripheral mu‐opioid receptors to the antinociception in rats with a spinal nerve ligation‐induced neuropathy. Results of the present study indicate that both spinal and peripheral opioid receptors may contribute to the opioid‐induced antinociception in the neuropathy. Further, mu‐opioid peptide ligands (DAMGO and endomorphins) are more effective than opioid alkaloids in relieving of neuropathic pain. Moreover, reduction of the mu‐opioid antinociceptive potency appears to be due to the fact that nerve injury reduced expression of mu‐opioid receptors in the spinal ganglia. Identification of the molecular mechanisms involved may be of importance to the understanding of the molecular mechanism of opioid action in neuropathic pain, as well as to the development of better and more effective treatment of neuropathic pain in humans.