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Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Socially induced morphine pseudosensitization in adolescent mice
Stephen R Hodgson1, Rebecca S Hofford, Kris W Roberts
1Behavioral and Cellular Neuroscience, Department of Psychology, Texas A&M University, College Station, Texas 77843, USA.
Abstract:
Given that social influences are among the strongest predictors of adolescents' drug use, this study examined the effect of social interaction on morphine-induced hyperlocomotion in both adolescent and adult mice. Three experimental groups of adolescent and adult male mice were examined (i) morphine-treated mice (twice daily, 10-40 mg/kg, subcutaneous), (ii) saline-injected mice housed together with the morphine-treated mice ('saline cage-mates'), and (iii) saline-injected mice housed physically and visually separated from the morphine-treated mice ('saline alone'). After the treatment period, mice were tested individually for their locomotor response to 10 mg/kg morphine (subcutaneous). Adolescent saline cage-mates, though administered morphine for the very first time, exhibited an enhanced hyperlocomotion response similar to the locomotor sensitization response exhibited by the morphine-treated mice. This was not observed in adults. In adults, there were no significant differences in morphine-induced hyperlocomotion between saline alone and saline cage-mates. As expected, morphine-treated adults and adolescents both exhibited locomotor sensitization. These results show a vulnerability to social influences in adolescent mice, which does not exist in adult mice.
Insights
Adolescent mice exposed to social cues from morphine-treated peers showed increased activity, unlike adults. This highlights adolescents' heightened vulnerability to social influences on drug responses.
Area of Science:
- Neuroscience
- Developmental Psychology
- Pharmacology
Background:
- Social influences significantly predict adolescent drug use.
- Understanding social effects on drug response is crucial for public health.
- Adolescent brains are uniquely sensitive to environmental and social factors.
Purpose of the Study:
- To investigate the impact of social interaction on morphine-induced hyperlocomotion in adolescent and adult mice.
- To determine if social exposure can induce a sensitization-like response to morphine in adolescents.
- To compare the effects of social context on drug response between adolescent and adult rodents.
Main Methods:
- Three groups of adolescent and adult male mice were used: morphine-treated, saline cage-mates, and saline alone.
- Mice received daily subcutaneous injections of morphine or saline over a treatment period.
- Locomotor activity was assessed individually after a final morphine challenge dose.
Main Results:
- Adolescent saline cage-mates exhibited enhanced hyperlocomotion to morphine, mimicking locomotor sensitization.
- Adult saline cage-mates did not show significant differences in morphine response compared to saline alone controls.
- Both morphine-treated adolescents and adults developed locomotor sensitization, as expected.
Conclusions:
- Adolescent mice display a significant vulnerability to social influences regarding drug-induced locomotor activity.
- This social influence effect on drug response is specific to the adolescent period and not observed in adults.
- Findings suggest that social context plays a critical role in shaping adolescent responses to drugs of abuse.
