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Updated: Nov 30, 2025
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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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Opioid-Induced Hyperalgesic Priming in Single Nociceptors
Eugen V Khomula1, Dionéia Araldi1, Ivan J M Bonet1
1Departments of Medicine and Oral and Maxillofacial Surgery, Division of Neuroscience, and UCSF Pain and Addiction Research Center, University of California at San Francisco, San Francisco, California 94143.
Summary
Opioid agonists like fentanyl can cause pain chronification through hyperalgesic priming. This study reveals specific nociceptor changes in an in vitro model, identifying cellular mechanisms in pain sensitization.
Area of Science:
- Neuroscience
- Pain Research
- Pharmacology
Background:
- Clinical opioid agonists, such as fentanyl, can induce hyperalgesic priming (HP), a maladaptive neuroplasticity leading to pain chronification.
- Understanding the specific nociceptor populations and mechanisms involved in opioid-induced hyperalgesic priming (OIHP) is crucial for developing targeted pain therapies.
Purpose of the Study:
- To establish and utilize an in vitro model of OIHP in male rats to identify involved nociceptor populations and maintenance mechanisms.
- To investigate cellular changes in dorsal root ganglion (DRG) neurons following in vivo opioid priming.
Main Methods:
- OIHP was induced in male rats via systemic fentanyl administration and confirmed by prolonged prostaglandin E2 (PGE2) hyperalgesia.
- In vitro experiments utilized small-diameter DRG neurons cultured from fentanyl-primed rats and rats treated with agents reversing Type I or Type II priming.
- Neuronal sensitization to PGE2 was assessed by measuring action potential (AP) rheobase, and neurons were classified by isolectin B4 (IB4) staining.
Main Results:
- Fentanyl-induced OIHP involved neuroplasticity in weakly IB4-positive and IB4-negative nociceptors, exhibiting properties of Type I and Type II priming.
- Enhanced PGE2 sensitization was observed in weakly IB4+ and IB4- neurons, which was attenuated by in vivo reversal agents.
- Strongly IB4-positive neurons showed enhanced sensitivity to a higher PGE2 concentration, with an unelucidated mechanism.
Conclusions:
- In vivo fentanyl administration induces persistent in vitro neuroplasticity in specific nociceptor populations (weakly IB4+ and IB4-), consistent with Type I and Type II priming.
- The findings highlight population-specific alterations in nociceptor sensitization contributing to opioid-induced hyperalgesia.
- Further research is needed to elucidate the mechanisms of enhanced PGE2 sensitivity in strongly IB4+ nociceptors.
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