Related Experiment Video

Updated: Sep 12, 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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Habenular μ-opioid receptor knockout and chronic systemic receptor blockade promote negative affect and heighten

Elizabeth A Pekarskaya, Julia Alexsandra Galiza Soares, Frances G Hough

    Biorxiv : the Preprint Server for Biology
    |August 6, 2025
    PubMed

    Insights

    Chronic disruption of the μ-opioid receptor (MOR) signaling in mice increases anxiety, reduces social behavior, and heightens pain sensitivity. The habenula is identified as a key brain region mediating these effects of opioid system dysfunction.

    Area of Science:

    • Neuroscience
    • Pharmacology
    • Behavioral Science

    Background:

    • The μ-opioid receptor (MOR) is crucial for mood and pain regulation, with dysfunction linked to psychiatric and nociceptive disorders.
    • The habenula, an epithalamic structure, is rich in MOR and implicated in aversive states.
    • Understanding MOR's role in specific brain regions is key to addressing mood and pain disorders.

    Purpose of the Study:

    • To investigate the behavioral consequences of sustained MOR signaling inhibition.
    • To identify key brain regions mediating the effects of disrupted MOR signaling.
    • To explore the role of the habenula in affective and nociceptive processing related to opioid signaling.

    Main Methods:

    • Adult C57BL/6J mice received acute or chronic administration of methocinnamox (MCAM), a MOR antagonist.
    • A comprehensive behavioral battery assessed affective, social, and pain behaviors.
    • Selective knockout of habenular MORs was performed in adult Oprm1fl/fl mice.

    Main Results:

    • Chronic MCAM administration induced anxiety-like behavior, decreased sociability, and enhanced mechanical allodynia and thermal hyperalgesia.
    • Acute MCAM blocked opioid-induced analgesia but did not alter baseline behavior.
    • Selective knockout of habenular MORs replicated key chronic MCAM-induced deficits, including anxiety and mechanical hyperalgesia.

    Conclusions:

    • Sustained inhibition of MOR signaling disrupts affective and nociceptive processing.
    • The habenula is a critical node mediating behavioral deficits associated with disrupted opioid signaling.
    • These findings highlight the habenula's importance in mood and pain regulation via the opioid system.

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