Interoceptive conditioning through repeated suppression of morphine-abstinence. II. Relapse-testing

Area of Science:

• Pharmacology
• Neuroscience
• Behavioral Science

Background:

• Physical dependence and tolerance to opioids like morphine are significant clinical concerns.
• Understanding the mechanisms of drug reinforcement is crucial for addiction research.
• Opioid withdrawal cycles may influence subsequent drug-seeking behavior.

Purpose of the Study:

• To investigate the conditioned reinforcing properties of etonitazene in rats with differing morphine administration histories.
• To determine if daily cycles of morphine abstinence and suppression generate latent conditioned reinforcement.
• To explore the transfer of conditioned reinforcement from morphine to etonitazene.

Main Methods:

• Rats were assigned to saline infusion, daily morphine injection, or continuous morphine infusion groups.
• Behavioral baselines for water reinforcement were established using lever pressing.
• Etonitazene was substituted for water, and consumption was measured over 20 weeks in relapse tests.

Main Results:

• The daily morphine injection group consumed significantly more etonitazene than the continuous infusion group.
• No significant differences in water consumption were observed between groups.
• These findings suggest the development of conditioned reinforcing properties specific to the injection regimen.

Conclusions:

• Daily cycles of morphine abstinence and suppression, experienced only by the injection group, likely generated conditioned reinforcing properties.
• These conditioned properties, linked to internal sensations of morphine, were transferred to etonitazene.
• The study provides evidence for interoceptive conditioning in opioid reinforcement and relapse.