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Genetic differences in morphine sensitivity, tolerance and withdrawal in rats
O Hoffmann1, A Plesan, Z Wiesenfeld-Hallin
1Department of Medical Laboratory Sciences and Technology, Division of Clinical Neurophysiology, Huddinge University Hospital, S-141 86 Huddinge, Sweden.
Brain Research
|September 18, 1998
Summary
Genetic variations in rats significantly impact their response to pain and morphine. Different rat strains exhibit distinct pain sensitivity, morphine effectiveness, and withdrawal symptoms, highlighting genetic influences on opioid responses.
Area of Science:
- Neuroscience
- Pharmacology
- Genetics
Background:
- Rodents exhibit genetic variability in their endogenous opioid systems and responses to pain.
- Understanding these differences is crucial for pain management research.
Purpose of the Study:
- To compare pain responses, morphine sensitivity, and opioid tolerance/dependence across three rat strains: spontaneously hypertensive (SHR), Wistar-Kyoto (WK), and Sprague-Dawley (SD).
Main Methods:
- Utilized the hot plate test to assess nociception.
- Administered morphine to evaluate antinociceptive effects and tolerance development.
- Induced withdrawal symptoms using naloxone to study dependence.
Main Results:
- Significant differences in basal nociception were observed, with SHRs being hypoalgesic compared to WK and SD rats.
- Morphine's antinociceptive effect varied by strain (SD > SHR > WK).
- Tolerance developed faster in WK rats than in SD and SHR rats, with SHRs showing hyperalgesia during tolerance development.
Conclusions:
- Rat genetic background profoundly influences nociception and responses to morphine.
- Observed strain-specific differences in morphine efficacy, tolerance, dependence, and withdrawal symptoms.
- These findings underscore the importance of genetic factors in opioid pharmacodynamics.