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Behavioral effects of low and high acute doses of morphine in solitary mice
Abstract:
The effects of morphine (5, 10, 100, and 150 mg/kg SC) on locomotor activity, object manipulation, grooming, rearing, and responsiveness to social stimulation were observed in naive, nontolerant mice. Morphine induced significant changes in the behavior elements recorded. Five and 10 mg/kg morphine caused an initial phase of about 1 h with inhibition of all activities. After 1 h the mice gradually increased activity and exceeded the corresponding placebo level at the end of the sessions. 100 and 150 mg/kg morphine caused an increase in locomotor activity. This hyperactive continuous running was stereotyped, restricted as it was to only a certain part of the experimental cage. Concurrently all other behavior elements were abolished. The animals did not normalize within the observation period. Neither the sedated mice with low doses nor the mice with high doses of morphine responded socially to the presence of another untreated mouse which was placed in the cage as a social response test.
Insights
Morphine significantly alters mouse behavior, with low doses causing initial sedation followed by hyperactivity, while high doses induce stereotyped running and abolish other behaviors. Social responsiveness was impaired across all tested morphine doses.
Area of Science:
- Neuroscience
- Pharmacology
- Animal Behavior
Background:
- Morphine is a potent opioid analgesic with known central nervous system effects.
- Understanding dose-dependent behavioral effects is crucial for clinical and research applications.
Purpose of the Study:
- To investigate the dose-dependent effects of subcutaneous morphine on various behavioral parameters in naive mice.
- To assess the impact of morphine on locomotor activity, object manipulation, grooming, rearing, and social responsiveness.
Main Methods:
- Naive, nontolerant mice were administered varying doses of morphine (5, 10, 100, 150 mg/kg, SC).
- Behavioral elements including locomotor activity, object manipulation, grooming, rearing, and social interaction were systematically recorded.
- A social response test was incorporated to evaluate interaction with an untreated conspecific.
Main Results:
- Low morphine doses (5, 10 mg/kg) initially inhibited activity, followed by a rebound hyperactivity exceeding placebo levels.
- High morphine doses (100, 150 mg/kg) resulted in stereotyped, continuous locomotor activity, suppressing all other observed behaviors.
- Social responsiveness was significantly impaired in mice treated with both low and high doses of morphine.
Conclusions:
- Morphine exhibits complex, dose-dependent effects on mouse behavior, ranging from initial sedation to pronounced stereotyped hyperactivity.
- Opioid administration, at the tested doses, significantly disrupts normal behavioral patterns, including social interaction.
- These findings highlight the critical influence of morphine dosage on neurobehavioral outcomes.