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Morphine-like stimulus effects in the monkey: opioids with antagonist properties
Pharmacology, Biochemistry, and Behavior
|February 1, 1981
Summary
Opioid drugs with mixed agonist and antagonist properties show varied effects in squirrel monkeys. These findings highlight the diverse nature of opioid stimulus effects and the need for cross-species research.
Area of Science:
- Pharmacology
- Neuroscience
- Behavioral Science
Background:
- Opioids exhibit a wide range of agonist and antagonist properties.
- Understanding these properties is crucial for drug development and therapeutic use.
- Previous research in rats has categorized opioid stimulus effects.
Purpose of the Study:
- To evaluate the discriminative stimulus properties of various opioids in squirrel monkeys.
- To compare opioid effects across species, specifically between rats and squirrel monkeys.
- To investigate the heterogeneous nature of opioid stimulus effects.
Main Methods:
- Squirrel monkeys were trained to discriminate between morphine and saline using a two-choice discrete-trial avoidance task.
- Stimulus control was established by consistent lever selection in drug or saline conditions.
- Generalization tests were performed with compounds previously characterized in rats.
Main Results:
- Profadol and WY-16,225 demonstrated morphine-like stimulus effects, equipotent to morphine.
- Naloxone antagonized morphine-appropriate responding, with higher doses needed for WY-16,225.
- Most other tested opioids showed partial morphine-like stimulus control, indicating heterogeneous effects.
Conclusions:
- Opioid discriminative stimulus effects are heterogeneous, even among compounds with mixed agonist/antagonist profiles.
- Interspecies comparisons are important for fully understanding opioid pharmacology.
- The study confirms the complexity of opioid receptor interactions and behavioral outcomes.