e20 Abstracts / Drug and Alcohol Dependence 146 (2015) e2–e33 Social interaction may reduce amphetamine reward in male adolescent rats by activating mesocorticolimbic dopamine systems Virginia G. Weiss, Rebecca S. Hofford, Justin R. Yates, M.T. Bardo Univeristy of Kentucky, Lexington, KY, United States Aims: One way to predict if an adolescent will initiate drug use is whether or not their peers use drugs. In animals, social facilitation of drug taking behavior is only beginning to be understood. Recent work indicated that adolescent rats raised in isolated conditions find social interactions to be highly reward- ing, especially in males. In a recent study in our laboratory, we found that individually housed adolescent male rats showed a conditioned place preference (CPP) for a compartment paired previously with a social partner. This social reward reduced amphetamine reward when rats were allowed choice between a social- and drug paired compartment concurrently. The cur- rent experiment tested the hypothesis that social interaction may compete with amphetamine reward by activating similar neural systems. Methods: Male adolescent Sprague Dawley rats (28 days of age, n = 16) were habituated to a CPP apparatus chamber for 30 min on the first session. The next session, half of the subjects were placed into a chamber alone for 30 min, while the other half were paired with a same-age male conspecific for 30 min. Immediately follow- ing the session, brains were dissected into medial prefrontal cortex (mPFC), dorsal striatum, nucleus accumbens (NAcc), and hypothal- amus; brain levels of dopamine, DOPAC, 5-HT, and 5-HIAA were quantified by HPLC-EC. Results: Results for dopamine utilization (DOPAC/DA) showed a main effect of brain region [F(3,10) = 88.957, p < 0.001] and a main effect of socialization [F(1,12) = 21.697, p = 0.001], with dopamine utilization elevated by social interaction across all regions. No significant effect of social interaction was observed with 5-HT uti- lization in any brain region examined. Conclusions: These results indicate that social interaction acti- vates mesocorticolimbic dopamine systems and that this neural activation may blunt the rewarding effect of amphetamine in ado- lescent male rats. Financial support: Funding provided by NIH grants P50 DA05312 and T32 DA016176 and R01 DA12964. http://dx.doi.org/10.1016/j.drugalcdep.2014.09.734 Choosing money over drugs: The underpinnings of rational choice in cocaine addicts Michael J. Wesley 1 , Terry Lohrenz 1 , Mikhail N. Koffarnus 1 , Samuel M. McClure 2 , Richard De La Garza II 3 , Thomas F. Newton 3 , Warren K. Bickel 1 , P. Read Montague 1 1 Virginia Tech Carilion Research Institute, Roanoke, VA, United States 2 Stanford University, Stanford, CA, United States 3 Baylor College of Medicine, Houston, TX, United States Aims: There is a tension between the idea of damaged decision- making systems in addicts and the observation that some choices are rational. Cocaine addiction is portrayed as the hijacking of valu- ation signals, such as those in the striatum, where addicts are driven to choose cocaine over non-drug alternatives. In a simple depic- tion of this claim, choices away from cocaine would not involve the striatum. Hence, our working hypothesis that choosing money over cocaine would not correlate with striatal activity but other reward-guided brain areas. Methods: Fifty human controls (Ctrls) and cocaine addicts (CAs) were scanned with fMRI during four inter-temporal choice tasks. Whereas single-commodity tasks (i.e., money now vs. money later, MM; and cocaine now vs. cocaine later, CC) have been used exten- sively, cross-commodity tasks (i.e., money now vs. cocaine later, MC; and cocaine now vs. money later, CM) have recently been designed to capture real-world trade-offs in addicts. The proportion of now and later choices was isolated and examined. Brain function was compared between groups while viewing and submitting now and later choices. Results: In single-commodity tasks, CAs made fewer future money choices than Ctrls (40% vs. 58%, P < .02) with no difference in future cocaine choices. In cross-commodity tasks, CAs made more cocaine choices (MC = 35%; CM = 50%) than Ctrls (MC = 17%; CM = 08%), however, a large portion of CAs choices was for money (MC = 65% and CM = 50%). Whole brain analyses (P < .005, FWE) showed CAs had greater striatal responses for viewing and sub- mitting money over cocaine choices, compared to Ctrls, and the left lateral prefrontal cortex was greater for future money choices. Conclusions: The striatum and lateral prefrontal cortex partici- pate in cocaine addicts forgoing cocaine for a non-drug alternative. These results highlight flexibility in addicts and provide context and targets for shifting choices from cocaine. Financial support: Supported by NIDA grants R01DA030241; R01DA024080; R01DA012997. http://dx.doi.org/10.1016/j.drugalcdep.2014.09.735 Effects of cannabis and cigarette smoking on gray matter volume: A voxel-based morphometry study Reagan R. Wetherill, K. Jagannathan, Joel Mumma, Barbara Johnson, Hengyi Rao, Anna Rose Childress, Teresa Franklin Psychiatry, University of Pennsylvania, Philadelphia, PA, United States Aims: Neuroimaging studies have provided evidence of gray matter volume differences in drug dependent individuals com- pared to healthy control groups; however, these studies may be confounded by differences between groups in cigarette depend- ence. To examine the effects of chronic cannabis use on gray matter volume and to control for the effects of cigarette smok- ing, this study examined differences in gray matter volume between demographically matched cannabis-dependent individ- uals, nicotine-dependent individuals, and healthy controls using optimized voxel-based morphometry. Methods: High-resolution T1 structural scans were obtained from cannabis-dependent individuals (n = 26), nicotine-dependent individuals (n = 26), and healthy controls (n = 26). Groups were matched on age, sex, and years of education. Structural scans were segmented and registered using DARTEL in SPM8. Whole- brain analyses were conducted in SPM8 using random field-based cluster-size testing and family-wise error rate correction for mul- tiple comparisons. Age, sex, and total gray matter volume were included as covariates. Results: Regional gray matter volume was greater among cannabis smokers in the right cerebellum than cigarette smokers. Cannabis smokers had less gray matter volume than controls in the orbitofrontal cortex. Cigarette smokers had less gray matter volume than controls in the thalamus and bilateral cerebellum.