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State dependent learning and morphine tolerance
1Department of Psychology, McMaster University, Hamilton, Ontario, Canada.
Behavioral Neuroscience
|April 1, 1988
Summary
Pentobarbital blocks morphine tolerance by altering drug cues, demonstrating state-dependent learning. This occurs because the anesthetic changes the context, preventing previously learned tolerance responses from being expressed.
Area of Science:
- Pharmacology
- Neuroscience
- Behavioral Science
Background:
- Morphine tolerance is influenced by Pavlovian conditioning, where cues predicting morphine elicit responses that reduce its effects.
- Previous studies suggest pentobarbital anesthesia can block analgesic tolerance to morphine in experienced rats.
Purpose of the Study:
- To investigate if pentobarbital's interference with morphine tolerance is due to state-dependent learning.
- To evaluate the role of altered predrug cues in the expression of morphine tolerance.
Main Methods:
- Rats received repeated morphine administrations, some signaled by pentobarbital.
- Tolerance was assessed by comparing analgesic responses to morphine in anesthetized and non-anesthetized conditions.
- The effect of pentobarbital cue presence/absence during testing was examined.
Main Results:
- Pentobarbital interfered with morphine tolerance in rats without prior barbiturate-opiate pairings.
- Morphine tolerance was observed when pentobarbital signaled both pretest and test morphine administrations.
- Omitting the pentobarbital cue during testing reduced tolerance in previously conditioned rats.
Conclusions:
- Pentobarbital-induced blockage of morphine tolerance is consistent with state-dependent learning.
- The anesthetic alters the environmental cues associated with morphine, impacting tolerance expression.
- Conditioning morphine effects to specific drug cues is crucial for tolerance development and expression.