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Behavioral effects of morphine, levorphanol, dextrorphan and naloxone in the frog Rana pipiens
Abstract:
Systemic morphine induces explosive motor behavior and generalized muscular rigidity in frogs. Naloxone does not reverse either of these effects of morphine but at high doses causes muscular flaccidity and unresponsiveness to stimulation. Intraspinal morphine induces rigidity, but not explosive motor behavior, and this action is blocked by naloxone. Behavioral effects are seen rarely after intraspinal levorphanol (rigidity) and never after intraspinal dextrorphan or naloxone. In contrast to systemic morphine and naloxone, systemic levorphanol and dextrorphan are lethal to frogs at high doses.
Insights
Systemic morphine causes motor and rigidity issues in frogs, which naloxone doesn't reverse. Intraspinal morphine causes rigidity blocked by naloxone, suggesting distinct pathways for these opioid effects.
Area of Science:
- Neuropharmacology
- Opioid receptor research
- Amphibian models
Background:
- Systemic morphine administration in frogs leads to significant motor disturbances and generalized muscle rigidity.
- Naloxone, an opioid antagonist, fails to reverse these morphine-induced effects and can cause flaccidity at high doses.
- Intraspinal administration of opioids reveals differential effects compared to systemic routes.
Purpose of the Study:
- To investigate the differential effects of systemic versus intraspinal morphine and related compounds on frog behavior.
- To determine the role of naloxone in reversing opioid-induced motor and rigidity effects.
- To explore the neuropharmacological mechanisms underlying opioid actions in a non-mammalian vertebrate model.
Main Methods:
- Administration of morphine, naloxone, levorphanol, and dextrorphan via systemic and intraspinal routes in frogs.
- Observation and documentation of behavioral responses, including motor activity and muscle tone.
- Assessment of the efficacy of naloxone in antagonizing opioid-induced effects.
Main Results:
- Systemic morphine induced explosive motor behavior and rigidity; naloxone did not reverse these.
- Intraspinal morphine caused rigidity, but not explosive behavior, and this was blocked by naloxone.
- Intraspinal levorphanol rarely caused rigidity, while dextrorphan and naloxone had no behavioral effects.
- Systemic levorphanol and dextrorphan were lethal to frogs at high doses, unlike systemic morphine and naloxone.
Conclusions:
- Opioid-induced motor behavior and rigidity in frogs involve distinct mechanisms, with intraspinal administration revealing naloxone-sensitive pathways for rigidity.
- The findings suggest differential receptor interactions or signaling pathways for systemic versus intraspinal opioid administration in amphibians.
- This study highlights the complexity of opioid pharmacology and provides insights into potential targets for managing opioid-induced side effects.