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Updated: May 27, 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

Regulation of rat MOR-1 gene expression after chronic intracerebroventricular administration of morphine

Zhi-Ping Zhu1, Ramesh B Badisa, Donald E Palm

  • 1College of Pharmacy and Pharmaceutical Sciences, Florida A and M University, Tallahassee, FL 32307, USA.

Molecular Medicine Reports
|November 18, 2011
PubMed

Insights

Morphine treatment down-regulates µ-opioid receptor mRNA in the rat hypothalamus, indicating tissue-specific adaptation and a role in neuroendocrine function.

Area of Science:

  • Neuroscience
  • Pharmacology
  • Molecular Biology

Background:

  • The µ-opioid receptor is the primary target for morphine's action.
  • Understanding opioid receptor regulation is crucial for managing pain and addiction.

Purpose of the Study:

  • To investigate the regulation of µ-opioid receptor mRNA levels in specific rat brain regions after chronic morphine administration.
  • To determine the tissue-specific effects of morphine on µ-opioid receptor gene expression.

Main Methods:

  • Intracerebroventricular administration of morphine to rats for 7 days.
  • Real-time quantitative RT-PCR analysis of µ-opioid receptor mRNA levels in the locus ceruleus, ventral tegmental area, nucleus accumbens, and hypothalamus.

Main Results:

  • Morphine treatment significantly down-regulated µ-opioid receptor mRNA levels in the hypothalamus.
  • µ-opioid receptor mRNA levels remained unchanged in the locus ceruleus, ventral tegmental area, and nucleus accumbens.

Conclusions:

  • Opioid-induced down-regulation of µ-opioid receptors in the hypothalamus suggests a role in neuroendocrine function.
  • Cellular adaptation to morphine tolerance is tissue-specific, varying across different brain regions.
Keywords:
μ-opioid receptorreal-time RT-PCRrat brainmorphinetolerance

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