• Stephen R Hodgson, Rebecca S Hofford, Kris W Roberts, Paul J Wellman, and Shoshana Eitan.
• Behavioral and Cellular Neuroscience, Department of Psychology, Texas A&M University, College Station, Texas 77843, USA.
• Behav Pharmacol. 2010 Mar 1; 21 (2): 112-20.

AbstractGiven 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.

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