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Pavlovian conditioning and addictive behavior: relapse to oral self-administration of morphine
Abstract:
The effect of conditional environmental stimuli on morphine consumption in rats was examined. Rats were first trained to consume a morphine solution (increased from 0.5 mg/ml to 1.2 mg/ml) by a forced drinking procedure spanning 235 days. Then, a period of abstinence of 81 days was given. They next received injections of morphine in one environment and injections of saline in a different environment (30 injections of morphine, dose increased from 5 mg/kg to 40 mg/kg). At the end of this phase, the effects of conditional environmental stimuli on tolerance to the analgesic effect of 40 mg/kg morphine were examined. Consistent with previous results, analgesic tolerance was most pronounced in the context of the cues previously associated with subcutaneous morphine injections. Finally, the effects of the different environments on consumption of morphine were determined in one-bottle and two-bottle tests. In a two-bottle test, there was almost no consumption of the morphine solution regardless of environment. In a one-bottle test, significantly more morphine was consumed in the drug environment than in the saline environment. The results are discussed in relation to theoretical views of the role of environmental stimuli in tolerance and drug dependence.
Insights
Environmental cues influence morphine tolerance and consumption. Rats showed increased analgesic tolerance and drug-seeking behavior in environments previously associated with morphine, highlighting the role of context in drug dependence.
Area of Science:
- Neuroscience
- Behavioral Pharmacology
- Addiction Research
Background:
- Environmental stimuli can play a significant role in drug-seeking behaviors and the development of tolerance.
- Understanding the influence of conditioned environmental cues is crucial for developing effective addiction treatments.
Purpose of the Study:
- To investigate the impact of conditional environmental stimuli on morphine consumption and analgesic tolerance in rats.
- To explore the role of environmental context in the development and expression of morphine dependence.
Main Methods:
- Rats were trained to consume morphine solutions, followed by a period of abstinence.
- Morphine injections were administered in one environment and saline in another, establishing environmental associations.
- Analgesic tolerance and morphine consumption were assessed in different environmental contexts using one-bottle and two-bottle tests.
Main Results:
- Analgesic tolerance to morphine was significantly more pronounced in the environment previously associated with drug administration.
- In a one-bottle test, morphine consumption was higher in the drug-associated environment compared to the saline environment.
- No significant morphine consumption was observed in a two-bottle test, irrespective of the environmental context.
Conclusions:
- Environmental stimuli act as powerful conditioned cues that influence both morphine tolerance and consumption.
- The findings support the role of environmental context in mediating drug dependence and withdrawal phenomena.
- These results have implications for understanding relapse prevention strategies in opioid addiction.