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Updated: Jun 17, 2026

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
07:23

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

Published on: July 29, 2014

[Expression of metabotropic glutamate receptor 5 in spinal cord of morphine tolerant rats]

Jin-Bian Liu1, Wei Jiang, Ai-Zhong Wang

  • 1Department of Anesthesiology, Shanghai Sixth People's Hospital, Shanghai Jiaotong University, Shanghai 200233, China.

Zhonghua Yi Xue Za Zhi
|January 12, 2010
PubMed
Abstract

Insights

Metabotropic glutamate receptor 5 (mGluR5) expression increases in morphine-tolerant rats. An mGluR5 antagonist, MPEP, prevents morphine tolerance by inhibiting mGluR5 expression in the spinal cord.

Area of Science:

  • Neuroscience
  • Pharmacology
  • Pain Research

Background:

  • Opioid tolerance is a significant clinical challenge, limiting long-term pain management.
  • Metabotropic glutamate receptor 5 (mGluR5) has been implicated in pain signaling and opioid-induced hyperalgesia.

Purpose of the Study:

  • To investigate the expression of mGluR5 in the spinal cord of rats with morphine tolerance.
  • To determine the effect of the mGluR5 antagonist MPEP on morphine tolerance and mGluR5 expression.

Main Methods:

  • A rat model of morphine tolerance was established through repeated intrathecal morphine administration.
  • The effects of MPEP on thermal pain threshold were assessed using the tail flick test.
  • Spinal cord mGluR5 expression was quantified using immunofluorescence and Western blot.

Main Results:

  • Chronic morphine administration led to decreased analgesic effect (tolerance) and increased mGluR5 expression in the spinal cord dorsal horn.
  • Co-administration of MPEP with morphine significantly attenuated the development of tolerance.
  • MPEP treatment reduced mGluR5 protein levels in morphine-tolerant rats.

Conclusions:

  • The mGluR5 antagonist MPEP effectively prevents the development of morphine tolerance.
  • Increased spinal mGluR5 expression is associated with morphine tolerance.
  • MPEP exerts its anti-tolerance effects by partially inhibiting mGluR5 expression in the spinal cord.

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