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Updated: Jul 29, 2026

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
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Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities

Published on: July 29, 2014

Tolerance and morphine-induced cross-tolerance are not shown to Tyr-W-MIF-1 analgesia

R L Bell1, A L Vaccarino, R D Olson

  • 1Department of Psychology, University of New Orleans, LA 70148, USA. ribell@iupui.edu

Peptides
|September 30, 1999
PubMed

Insights

This study investigated tolerance and cross-tolerance between Tyr-W-MIF-1 (a mixed agonist/antagonist) and morphine in rats. Results indicate distinct tolerance patterns, with Tyr-W-MIF-1 showing cross-tolerance to morphine but not vice versa.

Area of Science:

  • Pharmacology
  • Neuroscience
  • Drug Dependence Research

Background:

  • Opioid analgesics like morphine are widely used but can lead to tolerance and dependence.
  • Tyr-W-MIF-1 is a novel peptide with mixed agonist/antagonist properties at opioid receptors.
  • Understanding cross-tolerance is crucial for developing safer and more effective pain management strategies.

Purpose of the Study:

  • To investigate the development of tolerance and cross-tolerance between Tyr-W-MIF-1 and morphine.
  • To examine opiate dependence induced by these compounds.
  • To compare the distinct pharmacological profiles of Tyr-W-MIF-1 and morphine regarding tolerance.

Main Methods:

  • Rats were pretreated with Tyr-W-MIF-1, morphine, or saline for four consecutive days.
  • On the fifth day, animals were tested for analgesia induced by Tyr-W-MIF-1 or morphine.
  • Naloxone-precipitated withdrawal was assessed to evaluate opiate dependence.

Main Results:

  • Both Tyr-W-MIF-1 and morphine pretreatment resulted in similar levels of opiate dependence.
  • Animals pretreated with Tyr-W-MIF-1 showed cross-tolerance to morphine analgesia but not tolerance to Tyr-W-MIF-1 itself.
  • Morphine-pretreated animals developed tolerance to morphine but did not exhibit cross-tolerance to Tyr-W-MIF-1 analgesia.

Conclusions:

  • Tolerance and morphine-induced cross-tolerance were not observed for Tyr-W-MIF-1 analgesia.
  • Tyr-W-MIF-1 exhibits a unique tolerance profile compared to morphine.
  • These findings suggest differential mechanisms underlying tolerance to Tyr-W-MIF-1 and morphine.

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