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Morphine state-dependent learning: interactions with alpha2-adrenoceptors and acute stress
H Homayoun1, S Khavandgar, M R Zarrindast
1Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
Behavioural Pharmacology
|February 11, 2003
Summary
Morphine state-dependent memory in mice involves alpha-adrenoceptors and stress. Yohimbine and clonidine modulated morphine
Area of Science:
- Neuroscience
- Pharmacology
- Behavioral Science
Background:
- Opioid drugs like morphine can induce state-dependent learning, where memory retrieval is contingent on the drug's presence during both learning and recall.
- Alpha-adrenoceptors and acute stress are known to influence memory processes, but their interaction with opioid-induced state-dependency is not fully understood.
Purpose of the Study:
- To investigate the role of alpha-adrenoceptors and acute restraint stress in morphine state-dependent memory of passive avoidance in mice.
- To explore the interplay between opioid receptors, adrenergic receptors, and stress in modulating learning and memory.
Main Methods:
- Mice were trained on a passive avoidance task following morphine administration.
- Memory retrieval was tested under various conditions including pre-test administration of morphine, yohimbine, clonidine, and acute restraint stress.
- Dose- and time-dependency of drug and stress effects were analyzed.
Main Results:
- Morphine administration facilitated memory retrieval in a dose- and time-dependent manner, which was reversible by yohimbine and clonidine.
- Pre-training clonidine induced amnesia, which was restored by subsequent morphine or clonidine administration and blocked by yohimbine.
- Acute stress during training impaired memory, but this impairment was reversed by pre-test morphine or clonidine. Pre-test stress also restored morphine-impaired memory.
Conclusions:
- The findings suggest a significant functional interaction between alpha-opioid receptors, alpha-adrenergic receptors, and acute stress in regulating state-dependent learning and memory.
- Adrenergic agents and stress can modulate opioid-induced memory effects, highlighting a complex neurobiological mechanism underlying state-dependent memory.