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Morphine withdrawal in vitro: potentiation of agonist-dependent polyphosphoinositide breakdown
D E Pellegrini-Giampietro1, M Ruggiero, S Giannelli
1Department of Preclinical and Clinical Pharmacology, University of Florence, Italy.
Abstract:
Naloxone (10(-5) -10(-9) M) significantly increased the K+ (30 mM)-induced release of [3H[noradrenaline when it was applied to cortical slices taken from morphine-dependent rats but did not change the release of transmitter when applied to slices prepared from non-dependent animals. Therefore, this preparation was considered suitable to study withdrawal-related events and was used to monitor the agonist-induced changes of phospholipase C activity in the withdrawal state. Noradrenaline (1-100 microM) and carbachol (50-500 microM), when applied to cortical slices preincubated with [3H]inositol or with [32P]orthophosphate, dose dependently increased the formation of labeled inositol phosphates or of phosphatidic acid. This confirmed that noradrenaline and carbachol increase phospholipase C activity. This increase was significantly enhanced by naloxone (10(-6) M) when the slices were taken from dependent animals. The results now reported show for the first time in mammalian tissues that opioid withdrawal is associated with changes of phosphoinositide metabolism.
Insights
Naloxone, an opioid antagonist, enhanced neurotransmitter release in morphine-dependent rats, indicating withdrawal-related changes. This study reveals opioid withdrawal alters phosphoinositide metabolism in mammalian tissues.
Area of Science:
- Neuroscience
- Pharmacology
- Biochemistry
Background:
- Morphine dependence leads to complex physiological changes.
- Understanding opioid withdrawal mechanisms is crucial for developing effective treatments.
- Phosphoinositide metabolism plays a role in cellular signaling pathways.
Purpose of the Study:
- To investigate the effects of naloxone on neurotransmitter release in morphine-dependent rats.
- To examine agonist-induced phospholipase C activity during opioid withdrawal.
- To determine if opioid withdrawal is associated with changes in phosphoinositide metabolism.
Main Methods:
- Utilized rat cortical slices from morphine-dependent and non-dependent animals.
- Measured potassium-induced [3H]noradrenaline release.
- Assessed agonist-induced phospholipase C activity by measuring labeled inositol phosphates and phosphatidic acid formation.
Main Results:
- Naloxone significantly increased [3H]noradrenaline release in dependent rat cortical slices.
- Noradrenaline and carbachol dose-dependently increased phospholipase C activity.
- Naloxone enhanced agonist-induced phospholipase C activity in slices from dependent animals.
Conclusions:
- The rat cortical slice preparation is suitable for studying withdrawal-related events.
- Opioid withdrawal is associated with significant alterations in phosphoinositide metabolism in mammalian tissues.
- These findings provide novel insights into the neurobiological underpinnings of opioid withdrawal.