• M L Shawn Bates, Michael A Emery, Paul J Wellman, and Shoshana Eitan.
• Behavioral and Cellular Neuroscience, Department of Psychology, Texas A&M University, 4235 TAMU, College Station, TX 77843, USA; Interdisciplinary Program in Neuroscience, Texas A&M Institute for Neuroscience (TAMIN), USA.
• Drug Alcohol Depend. 2014 Sep 1;142:283-9.

BackgroundAdolescent opioid abuse is on the rise, and current treatments are not effective in reducing rates of relapse. Our previous studies demonstrated that social housing conditions alter the acquisition rate of morphine conditioned place preference (CPP) in adolescent mice. Specifically, the acquisition rate of morphine CPP is slower in morphine-treated animals housed with drug-naïve animals. Thus, here we tested the effect of social housing conditions on the development of morphine dependence and the extinction rate of an acquired morphine CPP.MethodsAdolescent male mice were group-housed in one of two housing conditions. They were injected for 6 days (PND 28-33) with 20 mg/kg morphine. Morphine only mice are animals where all four mice in the cage received morphine. Morphine cage-mate mice are morphine-injected animals housed with drug-naïve animals. Mice were individually tested for spontaneous withdrawal signs by quantifying jumping behavior 4, 8, 24, and 48 h after the final morphine injection. Then, mice were conditioned to acquire morphine CPP and were tested for the rate of extinction.ResultsMorphine cage-mates express less jumping behavior during morphine withdrawal as compared to morphine only mice. As expected, morphine cage-mate animals acquired morphine CPP more slowly than the morphine only animals. Additionally, morphine cage-mates extinguished morphine CPP more readily than morphine only mice.ConclusionsSocial housing conditions modulate morphine dependence and the extinction rate of morphine CPP. Extinction testing is relevant to human addiction because rehabilitations like extinction therapy may be used to aid human addicts in maintaining abstinence from drug use.Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

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