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Updated: Dec 7, 2025

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

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Quantitative Analysis of MOR-1 Internalization in Spinal Cord of Morphine-Tolerant Mice

Vittoria Borgonetti1, Nicoletta Galeotti2

  • 1Department of Neurosciences, Psychology, Drug Research and Child Health (Neurofarba), University of Florence, Florence, Italy.

Methods in Molecular Biology (Clifton, N.J.)
|September 25, 2020
PubMed

Insights

Opioid analgesic tolerance mechanisms are unclear. This study investigates the location of the mu-opioid receptor (MOR-1) in mice after repeated morphine exposure, suggesting receptor internalization as a key factor.

Area of Science:

  • Neuroscience
  • Pharmacology
  • Molecular Biology

Background:

  • Opioid analgesic tolerance is a complex biological process with incompletely understood mechanisms.
  • Opioid receptor desensitization is a critical aspect of tolerance, with receptor internalization being a leading hypothesis.
  • Understanding these mechanisms is crucial for managing pain and opioid dependence.

Purpose of the Study:

  • To investigate the localization of the mu-opioid receptor 1 (MOR-1) following repeated morphine administration.
  • To explore the role of receptor internalization in the development of morphine tolerance.
  • To establish a simple in vitro protocol for studying MOR-1 localization in vivo.

Main Methods:

  • Utilized a morphine-tolerant mouse model.
  • Administered morphine repeatedly to induce tolerance.
  • Employed western blotting and immunofluorescence techniques.
  • Analyzed MOR-1 localization in the spinal cord tissue.

Main Results:

  • Demonstrated a method to track MOR-1 localization in the spinal cord of tolerant mice.
  • Provided evidence for changes in MOR-1 distribution after chronic morphine exposure.
  • The study protocol successfully investigated receptor internalization.

Conclusions:

  • Receptor internalization is a plausible mechanism contributing to opioid analgesic tolerance.
  • The developed in vitro protocol offers a valuable tool for future research on opioid receptor dynamics.
  • Further elucidation of MOR-1 trafficking is essential for understanding and treating opioid tolerance.
Keywords:
InternalizationMorphineToleranceμ-Opioid receptor

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