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Updated: Aug 13, 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

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Opioid tolerance and the emergence of new opioid receptor-coupled signaling

A R Gintzler1, S Chakrabarti

  • 1Department of Biochemistry, State University of New York Health Science Center at Brooklyn, 11203, USA. agintzler@netmail.hscbklyn.edu

Molecular Neurobiology
|May 1, 2001
PubMed

Insights

Opioid tolerance involves more than reduced receptor function; it also stems from altered signaling pathways. Chronic morphine exposure shifts cellular signaling, revealing the adaptive plasticity of opioid systems.

Area of Science:

  • Neuroscience
  • Pharmacology
  • Molecular Biology

Background:

  • Chronic opioid exposure induces cellular adaptations like reduced receptor availability and G-protein function, traditionally viewed as opioid desensitization.
  • Emerging evidence suggests opioid tolerance is also driven by qualitative alterations in opioid signaling pathways.

Purpose of the Study:

  • To review evidence indicating that opioid tolerance results from both impaired receptor functionality and modified downstream signaling consequences.
  • To explore the molecular underpinnings of altered opioid signaling, focusing on changes in effector molecules coupled to the opioid receptor/G-protein pathway.

Main Methods:

  • Review of existing literature on cellular adaptations to chronic opioid exposure.
  • Analysis of molecular changes in opioid receptor/G-protein signaling pathways, including adenylyl cyclase activity and phosphorylation states.

Main Results:

  • Chronic morphine exposure leads to upregulation and increased phosphorylation of adenylyl cyclase type II isoforms.
  • A significant shift in opioid receptor/G-protein signaling occurs, moving from predominantly inhibitory Gialpha to stimulatory Gbetagamma subunits.
  • These adaptations highlight the plasticity of opioid signal transduction mechanisms.

Conclusions:

  • Opioid tolerance is a complex phenomenon involving both desensitization and altered signaling pathways.
  • Chronic morphine exposure induces adaptive changes in cellular signaling, enabling new signaling strategies and demonstrating the dynamic nature of opioid systems.

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