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Morphine antagonizes pentobarbital-induced anesthesia
Abstract:
Morphine was administered by the intracerebroventricular (i.c.v.) route to pentobarbital-anesthetized rabbits. Small doses of morphine (less than 150 micrograms) potentiated, but larger doses (greater than 250 micrograms) shortened, the duration of anesthesia. In naltrexone-pretreated animals, all doses of morphine employed acted only as an analeptic. Atropine, but not atropine methylbromide, blocked the analeptic effect of morphine, indicating that a central cholinergic mechanism was involved in this response. Tolerance to the analeptic effect was not evident. These results suggest that morphine exerts an arousal action which is usually masked by the dominant narcotic properties, but which becomes evident when administered intracerebroventricularly or in the presence of naltrexone.
Insights
Intracerebroventricular morphine in rabbits had dual effects on anesthesia duration. Naltrexone revealed morphine
Area of Science:
- Neuropharmacology
- Anesthesiology
Background:
- Morphine is a potent opioid analgesic with known central nervous system effects.
- Its influence on anesthesia duration and arousal is complex and dose-dependent.
Purpose of the Study:
- To investigate the central effects of morphine on pentobarbital-induced anesthesia in rabbits.
- To explore the role of opioid receptors and cholinergic mechanisms in morphine's central actions.
Main Methods:
- Morphine was administered intracerebroventricularly (i.c.v.) to pentobarbital-anesthetized rabbits.
- Dose-response effects on anesthesia duration were assessed.
- The influence of naltrexone pretreatment and atropine was examined.
Main Results:
- Low-dose i.c.v. morphine potentiated anesthesia; high-dose i.c.v. morphine shortened it.
- Naltrexone pretreatment reversed all morphine doses to an analeptic (arousal) effect.
- Atropine, but not atropine methylbromide, blocked this analeptic effect, suggesting a central cholinergic pathway.
Conclusions:
- Morphine possesses a central arousal action, typically masked by its narcotic effects.
- This arousal effect is unmasked by i.c.v. administration or opioid receptor blockade with naltrexone.
- A central cholinergic mechanism mediates morphine's analeptic effect.