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Morphine tolerance in arthritic rats and serotonergic system
1Department of Anesthesiology, Chung-Gung Memorial Hospital, Tao-Yuan, Taiwan, ROC.
Life Sciences
|March 30, 1999
Summary
Chronic inflammation accelerates morphine tolerance development in rats. This involves increased serotonin turnover in the spinal cord, suggesting a role for serotonin in pain and tolerance.
Area of Science:
- Neuroscience
- Pharmacology
- Pain Research
Background:
- Opioid analgesics like morphine are crucial for pain management.
- Developing tolerance to morphine limits its long-term effectiveness.
- Chronic inflammation is a common condition associated with persistent pain.
Purpose of the Study:
- To investigate the impact of chronic inflammation on the development of morphine tolerance.
- To explore the neurochemical changes in the spinal cord associated with inflammation and morphine tolerance.
Main Methods:
- Utilized the tail-flick test to assess morphine's analgesic effect in arthritic rats.
- Measured spinal cord monoamines and amino acid neurotransmitters.
- Compared tolerance development in arthritic rats versus vehicle-treated controls.
Main Results:
- Chronic inflammation significantly attenuated morphine's antinociceptive effect, leading to faster tolerance development.
- Arthritic rats showed an increased ratio of 5-hydroxyindole-3-acetic acid/5-hydroxytryptamine (5-HIAA/5-HT) in the lumbar spinal cord.
- No significant changes in norepinephrine, glutamate, aspartate, or GABA concentrations were observed.
- Morphine treatment increased serotonin turnover in the spinal cord of both control and arthritic rats.
Conclusions:
- Chronic inflammation accelerates the development of morphine tolerance.
- Increased serotonin turnover in the spinal cord plays a significant role in chronic pain and morphine tolerance.
- Serotonin up-regulation is a key mechanism underlying morphine tolerance in the context of chronic inflammation.