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Persistence and specificity of small doses of morphine on intake of alcoholic beverages
Abstract:
Subsequent to water deprivation, male rats were given daily, 1.5-hr opportunities to take either water or a sweetened ethanol solution (ES). Each day, 15 min before the session, rats received a subcutaneous injection of either morphine (1.0 mg/kg) or saline. Across daily sessions, rats given saline gradually increased their intake of ES, until they were eventually taking about 2.0 to 3.0 g of ethanol/kg a session. Rats receiving morphine took greater amounts of ES from nearly the first opportunities. Additional tests assessed the effects of small doses of morphine on intakes of some sucrose solutions, and sweetened solutions containing methanol or propanol. The data support the conclusion that small doses of morphine persistently increase intake of ES across many days (up to 100) of testing, but that the effect is not unique to ES. Even though morphine's effects are not specific to ethanol, the fact that morphine persistently increases intake of ES is of interest with respect to theories of alcoholism.
Insights
Small doses of morphine persistently increase the intake of sweetened ethanol solutions in male rats. This effect, observed over extended testing periods, is not exclusive to ethanol, suggesting broader implications for understanding substance use behaviors.
Area of Science:
- Pharmacology
- Neuroscience
- Animal Behavior
Background:
- Ethanol consumption is a complex behavior influenced by various factors.
- Understanding the neurobiological underpinnings of substance intake is crucial for developing effective interventions.
Purpose of the Study:
- To investigate the effects of morphine on ethanol solution intake in male rats.
- To determine if morphine's effect on ethanol intake is specific to ethanol or extends to other palatable solutions.
Main Methods:
- Male rats were water-deprived and given daily access to water or a sweetened ethanol solution (ES).
- Rats received daily subcutaneous injections of morphine (1.0 mg/kg) or saline prior to sessions.
- Intake of ES and other solutions (sucrose, methanol, propanol) was measured across multiple days.
Main Results:
- Rats treated with saline gradually increased ES intake over sessions.
- Rats treated with morphine showed significantly higher ES intake from early sessions.
- Morphine also increased the intake of sucrose, methanol, and propanol solutions, indicating a non-specific effect.
Conclusions:
- Low doses of morphine persistently enhance the intake of sweetened ethanol solutions in rats.
- Morphine's effect on intake is not specific to ethanol, suggesting a broader influence on the consumption of palatable substances.
- These findings offer insights into the neurobiological mechanisms potentially relevant to alcoholism and substance use disorders.