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Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
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Chronic morphine drinking establishes morphine tolerance, but not addiction in Wistar rats

Ralf Binsack1, Ming-lan Zheng, Zhan-sai Zhang

  • 1Department of Toxicology, School of Medicine, Zhejiang University, Hangzhou 310006, China.

Journal of Zhejiang University. Science. B
|October 19, 2006
PubMed
Abstract

Insights

Chronic morphine consumption in drinking water did not induce addiction in Wistar rats, despite causing tolerance and weight loss. This suggests current animal models for morphine addiction may need re-evaluation.

Area of Science:

  • Pharmacology
  • Neuroscience
  • Animal Models

Background:

  • Morphine addiction is a significant public health issue.
  • Existing animal models for inducing morphine addiction have yielded conflicting results.
  • Understanding reliable methods to model addiction is crucial for developing effective treatments.

Purpose of the Study:

  • To investigate whether chronic morphine consumption via drinking water can induce addiction in Wistar rats.
  • To assess the validity of using sweetened drinking water as a method for morphine self-administration in animal studies.
  • To determine if observed physiological changes correlate with addictive behavior.

Main Methods:

  • Wistar rats received daily morphine (35 mg/kg) in sugar water for three weeks, with controls receiving sugar water only.
  • Morphine tolerance was assessed using the tail immersion test post-treatment.
  • A two-day preference test evaluated the rats' choice between sugar water with and without morphine after a one-week withdrawal period.

Main Results:

  • Chronic morphine intake resulted in decreased body weight and the development of morphine tolerance.
  • Despite tolerance, Wistar rats did not exhibit a preference for the morphine-laced sugar water during the preference phase.
  • Physiological changes like tolerance did not equate to behavioral signs of addiction.

Conclusions:

  • Body weight reduction and tolerance do not necessarily indicate morphine craving or addiction.
  • The current animal model using morphine in drinking water may not be effective in establishing morphine addiction.
  • Re-evaluation of animal models is necessary to accurately study and treat morphine addiction.

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