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Updated: Jan 10, 2026
Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Methadone and morphine have equivalent analgesic but not reward potency in female mice
Akash Shanmugam1, Samantha O Vanderhoof1, Michael A Kelberman1,2
1Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA.
Background:
Morphine is a potent opioid analgesic but carries high abuse potential. Some evidence indicates that the opioid methadone, used in maintenance therapy for opioid dependence, also provides analgesia with lower misuse liability, but direct behavioral comparisons of morphine and methadone under matched conditions remain limited.
Methods:
Dose responses curves for morphine and methadone (0.3-10 mg/kg) were generated in adult female C57BL6/J mice using paradigms to measure reward (conditioned place preference) and analgesia (von Frey and hot plate).
Results:
Morphine supported a conditioned place preference at all doses tested, while methadone induced a significant place preference at 1 and 10 mg/kg, but not at 0.3 mg/kg. Both opioids increased mechanical and thermal antinociceptive thresholds only at the highest dose tested (10 mg/kg).
Conclusions:
These findings demonstrate that methadone has a lower reward, but similar analgesic potency compared to morphine in female mice.
Insights
Methadone exhibits lower reward potential than morphine, suggesting reduced abuse liability. Both opioids provided similar pain relief (analgesia) in female mice at high doses.
Area of Science:
- Pharmacology
- Neuroscience
- Pain Management
Background:
- Morphine is a powerful pain reliever with significant abuse potential.
- Methadone, used for opioid dependence, may also offer analgesia with less misuse risk.
- Direct comparisons of morphine and methadone's behavioral effects are limited.
Purpose of the Study:
- To directly compare the reward and analgesic effects of morphine and methadone.
- To evaluate the potential for reduced misuse liability of methadone versus morphine.
Main Methods:
- Dose-response curves (0.3-10 mg/kg) for morphine and methadone were established in female mice.
- Reward was assessed using conditioned place preference.
- Analgesia was measured using mechanical (von Frey) and thermal (hot plate) tests.
Main Results:
- Morphine induced reward at all tested doses.
- Methadone induced reward only at higher doses (1 and 10 mg/kg).
- Both morphine and methadone produced analgesia only at the highest dose (10 mg/kg).
Conclusions:
- Methadone demonstrates a lower reward effect compared to morphine in female mice.
- Methadone shows comparable analgesic potency to morphine.
- Findings suggest methadone may have a reduced abuse potential while maintaining analgesic efficacy.
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