The central versus peripheral antinociceptive effects of μ-opioid receptor agonists in the new model of rat visceral pain

Mahmoud Al-Khrasani, Erzsébet Lackó, Pál Riba, Kornél Király, Melinda Sobor, Júlia Timár, Shaaban Mousa, Michael Schäfer, Susanna Fürst

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18 Citations (Scopus)


This study describes the antinociceptive effects of μ-opioid agonists, d-Ala 2,N-Me-Phe 4,Gly 5-ol-enkephalin (DAMGO) and morphine in a model of rat visceral pain in which nociceptive responses were triggered by 2% acetic acid intraperitoneal (i.p.) injections. DAMGO and morphine were administered i.p., to the same site where acetic acid was delivered or intracerebroventricularly (i.c.v.). The antinociceptive actions of i.p. versus i.c.v. administered DAMGO or morphine were evaluated in the late phase of permanent visceral nociceptive responses. Both compounds inhibited the nociceptive responses in a dose-dependent manner and exhibited more potent agonist activity after i.c.v. than i.p. administration. DAMGO and morphine showed comparable ED 50 values after i.p. injections. However, DAMGO was much stronger than morphine after central administration.Co-administration of the peripherally restricted opioid antagonist, naloxone methiodide (NAL-M), significantly attenuated the antinociceptive effects of i.p. DAMGO or morphine. On the other hand, i.c.v. injections of NAL-M partially antagonized the antinociceptive effect of i.p. morphine and failed to affect the antinociceptive action of i.p. DAMGO indicating the partial and pure peripheral antinociceptive effects of morphine and DAMGO, respectively.These results suggest the role of either central or peripheral μ-opioid receptors (MOR) in mediating antinociceptive effects of i.pμ-opioid agonists in the rat late permanent visceral pain model which closely resembles the clinical situation.

Original languageEnglish
Pages (from-to)238-243
Number of pages6
JournalBrain Research Bulletin
Issue number2-3
Publication statusPublished - Feb 10 2012



  • Antinociception
  • Morphine
  • Peripheral MOR
  • Rat acetic acid induced late permanent visceral pain

ASJC Scopus subject areas

  • Neuroscience(all)

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