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Updated: Apr 29, 2026

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
07:23

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities

Published on: July 29, 2014

34.8K

Toll-like receptor 4 mutant and null mice retain morphine-induced tolerance, hyperalgesia, and physical dependence

Theresa Alexandra Mattioli1, Heather Leduc-Pessah2, Graham Skelhorne-Gross3

  • 1Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada.

Plos One
|May 15, 2014
PubMed

Insights

Toll-like receptor 4 (TLR4) does not influence morphine tolerance, hyperalgesia, or physical dependence. Studies in TLR4 mutant and null mice show no impact on opioid-induced effects, suggesting TLR4 is not essential for these responses.

Area of Science:

  • Neuroscience
  • Immunology
  • Pharmacology

Background:

  • The innate immune system, particularly toll-like receptor 4 (TLR4), plays a role in modulating central nervous system responses to opioids.
  • Understanding TLR4's contribution to opioid-induced effects is crucial for managing pain and addiction.

Purpose of the Study:

  • To investigate the role of toll-like receptor 4 (TLR4) in the development of morphine tolerance, hyperalgesia, and physical dependence.
  • To compare these effects in mice with non-functional or absent TLR4.

Main Methods:

  • Utilized two inbred mouse strains: C3H/HeJ (dominant negative Tlr4 mutation) and B10ScNJ (TLR4 null mutants).
  • Assessed acute antinociception, analgesic tolerance, opioid-induced hyperalgesia, and physical dependence (naloxone-precipitated withdrawal).
  • Examined the effects of (-) naloxone and (+) naloxone stereoisomers on opioid-induced hyperalgesia.

Main Results:

  • TLR4 genotype did not affect acute antinociceptive responses to morphine.
  • The development of analgesic tolerance to repeated morphine treatment was independent of TLR4 status.
  • Opioid-induced hyperalgesia and physical dependence were not altered in TLR4 mutant or null mice.
  • Both naloxone stereoisomers suppressed opioid-induced hyperalgesia in all mouse strains tested.

Conclusions:

  • Toll-like receptor 4 (TLR4) is not required for the development of morphine tolerance.
  • TLR4 does not play a significant role in opioid-induced hyperalgesia or physical dependence.
  • These findings suggest that TLR4 is not a critical mediator of common opioid-induced adverse effects.

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