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Evidence from rats that morphine tolerance is a learned response
Journal of Comparative and Physiological Psychology
|July 1, 1975
Summary
Morphine tolerance develops through a conditioned hyperalgesic response linked to administration cues. This conditioned response can be extinguished by presenting cues without the drug, demonstrating a psychological component to analgesic tolerance.
Area of Science:
- Pharmacology
- Neuroscience
- Behavioral Science
Background:
- Successive administrations of morphine can lead to reduced analgesic effects, a phenomenon known as analgesic tolerance.
- The mechanism underlying analgesic tolerance is complex and may involve both physiological and psychological factors.
Purpose of the Study:
- To investigate the role of conditioned responses in the development of analgesic tolerance to morphine.
- To determine if environmental cues associated with morphine administration can elicit compensatory hyperalgesic responses.
Main Methods:
- Utilizing the hot plate test in rats to assess analgesia.
- Manipulating environmental cues predictive of morphine administration.
- Observing responses to placebo administration in the presence of drug-associated cues.
Main Results:
- Development of analgesic tolerance was observed and found to be dependent on reliable environmental cues predicting morphine's effects.
- Morphine-tolerant rats exhibited a hyperalgesic conditioned response when drug administration cues were followed by a placebo.
- Repeated presentation of drug-associated cues with a placebo led to the extinction of morphine tolerance.
Conclusions:
- The findings support a conditioning view of analgesic tolerance, suggesting that a conditioned hyperalgesic response plays a significant role.
- Environmental cues associated with drug administration can elicit compensatory responses that contribute to tolerance.
- Tolerance to morphine is not solely a direct pharmacological effect but is influenced by learned associations and conditioned responses.