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The role of 5-HT in the expression of morphine withdrawal in mice
1Department of Pharmacology, Faculty of Medicine, Al-Arab Medical University, Benghazi, Libya.
Abstract:
The effects of methysergide and cyproheptadine on naloxone-precipitated withdrawal symptoms were studied in morphine-dependent mice. The effects of these drugs were investigated both in normal mice and also mice injected with 6-OHDA intracerebrally to destroy the central noradrenergic neurones and examine whether 5-HT mediated effects are somehow linked to noradrenergic pathways. Methysergide given 30 min before naloxone attenuated withdrawal jumping, "wet dog" shakes, burrowing and body weight loss but aggravated hypothermia. Similar effects were produced by cyproheptadine on withdrawal "wet dog" shakes and hypothermia. Jumping was aggravated by low doses and attenuated by higher doses of cyproheptadine. Intracerebral injection of 6-OHDA in 5 days old mice pups resulted in hyperlocomotion by the end of 30 days before initiation of morphine dependence. When they were made morphine-dependent, mice pretreated with 6-OHDA developed higher degree of naloxone-induced withdrawal jumping than non-treated mice. Methysergide further aggravated jumping but its effect on both "wet dog" shakes and burrowing was lost in mice exposed to 6-OHDA. These findings suggest that 5-HT receptors are involved in the expression of withdrawal symptoms and the functional responsiveness of these receptors is dependent on intact nonadrenergic pathways.
Insights
Methysergide and cyproheptadine impact opioid withdrawal symptoms in mice. Serotonin receptor function in withdrawal is linked to noradrenergic pathways, influencing symptom severity.
Area of Science:
- Neuropharmacology
- Opioid Research
- Serotonin and Noradrenergic Systems
Background:
- Opioid withdrawal involves complex neurochemical changes.
- Serotonin (5-HT) and noradrenergic pathways are implicated in modulating these symptoms.
- Understanding these interactions is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the role of serotonin receptors in morphine withdrawal using methysergide and cyproheptadine.
- To examine the influence of noradrenergic pathways on serotonin-mediated withdrawal effects.
- To elucidate the interplay between 5-HT and noradrenergic systems in opioid dependence.
Main Methods:
- Morphine-dependent mice were used to study naloxone-precipitated withdrawal.
- Drugs targeting serotonin receptors (methysergide, cyproheptadine) were administered.
- Central noradrenergic neurons were destroyed using 6-hydroxydopamine (6-OHDA) in mice.
- Behavioral and physiological withdrawal symptoms were assessed.
Main Results:
- Methysergide and cyproheptadine differentially affected various withdrawal symptoms like jumping, shakes, burrowing, and body weight.
- Noradrenergic neuron destruction (6-OHDA) altered baseline locomotion and exacerbated withdrawal jumping.
- The efficacy of methysergide on certain withdrawal symptoms was diminished in 6-OHDA-treated mice.
- Hypothermia was aggravated by methysergide and cyproheptadine.
Conclusions:
- Serotonin receptors play a significant role in the manifestation of opioid withdrawal symptoms.
- The functional activity of these serotonin receptors is dependent on the integrity of noradrenergic pathways.
- Findings suggest a critical interaction between 5-HT and noradrenergic systems in opioid withdrawal.