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Differential up-regulation of microsomal and synaptic membrane mu opioid receptors

A M Moudy, J W Spain, C J Coscia

    Biochemical and Biophysical Research Communications
    |October 30, 1985
    PubMed

    Insights

    Naltrexone treatment increased mu opioid receptor levels in rat brain microsomes and synaptic membranes. Receptor binding affinity remained unaffected by the 7-day drug administration.

    Area of Science:

    • Neuroscience
    • Pharmacology
    • Molecular Biology

    Background:

    • Opioid receptors are crucial for pain modulation and reward pathways.
    • Understanding opioid receptor regulation is key to developing effective addiction treatments.
    • Naltrexone is an opioid antagonist used in managing opioid and alcohol dependence.

    Purpose of the Study:

    • To investigate the effect of naltrexone administration on mu opioid receptor levels in specific rat brain subcellular fractions.
    • To determine if naltrexone alters the binding affinity of mu opioid receptors.

    Main Methods:

    • Rats received naltrexone (5 mg/kg/day) via osmotic minipump for 7 days.
    • Forebrain mu opioid receptor concentrations were measured using homologous displacement assays with [3H]D-ala2-mePhe4-gly-ol5 enkephalin.
    • Receptor levels were quantified in crude membranes, synaptic plasma membranes, and microsomes.

    Main Results:

    • Naltrexone significantly increased mu opioid receptor concentrations in all measured fractions.
    • Microsomal fractions showed the most substantial increase (92% rise), followed by synaptic plasma membranes (51% rise).
    • Crude membranes exhibited a 77% increase in receptor levels, while binding affinities remained unchanged.

    Conclusions:

    • Short-term naltrexone administration upregulates mu opioid receptors in rat forebrain, particularly in microsomes.
    • This upregulation occurs without altering the receptor's binding affinity.
    • Findings suggest adaptive changes in opioid receptor expression in response to naltrexone blockade.

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