Related Experiment Videos
Chronic morphine administration decreases 5-hydroxytryptamine and 2-hydroxyindoleacetic acid content in the brain of
Abstract:
To study the effects of chronic morphine treatment on cerebral 5-hydroxytryptamine (5HT) metabolism morphine was administered twice daily for 5 or 8 weeks to male Wistar rats. Control rats were treated with 0.9% NaCl solution for the same period. In rats treated chronically with morphine for 8 weeks the cerebral concentrations of 5HT and 5HIAA were reduced by 12--15% (P less than 0.05) at 26--28 h after the last morphine injection (50 mg/kg s.c.). No such decrease was found in the brain of rats treated with morphine for 5 weeks. A test dose of morphine (30 mg/kg s.c. 2h) increased the cerebral concentration and probenecid-induced accumulation of 5HIAA in the rats treated with morphine for 8 weeks almost as much as in the brain of the control rats. Naloxone (10 mg/kg s.c. 2h) did not cause clear changes in the cerebral 5HT or 5HIAA concentration. These experiments suggest that endogenous opioid mechanisms are concerned in the regulation of 5HT neurons and that prolonged morphine treatment weakens these mechanisms. This weakening of endogenous regulation of 5HT neurons, which, however, still respond to acute morphine administration, might be part of the mechanism of compulsive drug use in narcotic addiction. It is possible that these neurons in dependent individuals do not function optimally without exogenous morphine. A similar phenomenon--weakening of endogenous regulation combined with clear responsivity to exogenous opiates--occurs in the cerebral dopamine neurons of rats treated chronically with narcotic analgesics.
Insights
Chronic morphine weakens brain serotonin regulation in rats, potentially contributing to addiction. This effect was observed after 8 weeks but not 5 weeks of treatment.
Area of Science:
- Neuroscience
- Pharmacology
- Neurochemistry
Background:
- Serotonin (5HT) plays a crucial role in brain function.
- Opioid drugs like morphine can influence neurotransmitter systems.
- Understanding the long-term effects of morphine on serotonin metabolism is important for addiction research.
Purpose of the Study:
- To investigate the impact of chronic morphine administration on cerebral 5-hydroxytryptamine (5HT) metabolism in male Wistar rats.
- To determine if prolonged morphine exposure alters endogenous opioid regulation of 5HT neurons.
Main Methods:
- Rats received daily morphine injections (50 mg/kg s.c.) twice daily for 5 or 8 weeks.
- Cerebral 5HT and 5-hydroxyindoleacetic acid (5HIAA) concentrations were measured at 26-28 hours post-injection.
- Acute morphine challenge and naloxone administration were used to assess neuronal responsiveness.
Main Results:
- Eight weeks of chronic morphine treatment significantly reduced cerebral 5HT and 5HIAA concentrations by 12-15% (P < 0.05).
- No significant changes were observed in rats treated for 5 weeks.
- Acute morphine administration still increased 5HIAA in chronically treated rats, indicating preserved responsiveness.
Conclusions:
- Prolonged morphine treatment (8 weeks) weakens endogenous opioid regulation of central serotonin (5HT) neurons.
- This desensitization of endogenous control, alongside maintained responsiveness to exogenous morphine, may contribute to compulsive drug use in addiction.
- Similar dysregulation is observed in dopamine neurons following chronic opioid exposure.