Early life adversity increases morphine tolerance and persistent inflammatory hypersensitivity through up-regulation of δ opioid receptors in mice

Sam Singleton, Claire C. Sneddon, Alice Bakina, Jeremy J. Lambert, Tim G. Hales (Lead / Corresponding author)

    Research output: Contribution to journalArticlepeer-review

    4 Citations (Scopus)
    99 Downloads (Pure)

    Abstract

    Exposure to severely stressful events during childhood is associated with poor health outcomes in later life, including chronic pain and substance use disorder. However, the mediators and mechanisms are unclear. We investigated the impact of a well-characterized mouse model of early-life adversity, fragmented maternal care (FC) between postnatal day 2 and 9, on nociception, inflammatory hypersensitivity, and responses to morphine. Male and female mice exposed to FC exhibited prolonged basal thermal withdrawal latencies and decreased mechanical sensitivity. In addition, morphine had reduced potency in mice exposed to FC and their development of tolerance to morphine was accelerated. Quantitative PCR analysis in several brain regions and the spinal cords of juvenile and adult mice revealed an impact of FC on the expression of genes encoding opioid peptide precursors and their receptors. These changes included enhanced abundance of δ opioid receptor transcript in the spinal cord. Acute inflammatory hypersensitivity (induced by hind paw administration of complete Freund's adjuvant) was unaffected by exposure to FC. However, after an initial recovery of mechanical hypersensitivity, there was a reappearance in mice exposed to FC by day 15, which was not seen in control mice. Changes in nociception, morphine responses, and hypersensitivity associated with FC were apparent in males and females but were absent from mice lacking δ receptors or β-arrestin2. These findings suggest that exposure to early-life adversity in mice enhances δ receptor expression leading to decreased basal sensitivity to noxious stimuli coupled with accelerated morphine tolerance and enhanced vulnerability to persistent inflammatory hypersensitivity.

    Original languageEnglish
    Pages (from-to)2253-2264
    Number of pages12
    JournalPain
    Volume164
    Issue number10
    Early online date10 May 2023
    DOIs
    Publication statusPublished - Oct 2023

    Keywords

    • Analgesia
    • Hyperalgesia
    • Neglect
    • Opiate
    • Pain

    ASJC Scopus subject areas

    • Clinical Neurology
    • Neurology
    • Anesthesiology and Pain Medicine

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