Local peripheral effects of μ-opioid receptor agonists in neuropathic pain in rats

https://doi.org/10.1016/j.neulet.2004.01.056Get rights and content

Abstract

Our study was designed to demonstrate peripheral antinociception of the μ-opioid receptor agonists: morphine (MF), [d-Ala2, N-Me-Phe4, Gly5-ol]enkephalin (DAMGO), endomorphin-1 (EM-1) and endomorphin-2 (EM-2) in Bennett's rat model of neuropathic pain. All the agonists were effective in antagonizing allodynia after their intraplantar (i.pl.) but not subcutaneous (s.c.) administration. Opioid peptides: DAMGO, EM-1 and EM-2 were more effective compared with corresponding doses of morphine (opioid alkaloid) in alleviating chronic pain. Peripheral μ-opioid receptors mediated the observed effects, as was evidenced by the i.pl. treatment with naloxone methiodide (active only at the site of injection) and by cyprodime, a selective μ-opioid receptor antagonist. These results have shown that opioid peptides are effective also after local treatment, and that their peripheral use may be of therapeutic interest in long-term management of chronic pain.

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Acknowledgments

Supported by grant PBZ-MN-001-/P05/2002 (I.O. and B.P.) and EU grant No. QLRT-2001-02919 (R.P.).

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