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Social dominance in rats: effects on cocaine self-administration, novelty reactivity and dopamine receptor binding and content in the striatum.

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Murray, Jennifer E 
Jordan, Emily R 
Xia, Jing 
Fluharty, Meg 


RATIONALE: Studies in human and non-human primates demonstrate that social status is an important determinant of cocaine reinforcement. However, it is unclear whether social rank is associated with other traits that also predispose to addiction and whether social status similarly predicts cocaine self-administration in rats. OBJECTIVES: The objective of this study is to investigate whether social ranking assessed using a resource competition task affects (i) the acquisition, maintenance and reinstatement of cocaine self-administration; (ii) the dopaminergic markers in the striatum; and (iii) the expression of ancillary traits for addiction. METHODS: Social ranking was determined in group-housed rats based upon drinking times during competition for a highly palatable liquid. Rats were then evaluated for cocaine self-administration and cue-induced drug reinstatement or individual levels of impulsivity, anxiety and novelty-induced locomotor activity. Finally, dopamine content, dopamine transporter (DAT) and dopamine D2/D3 (D2/3) receptor binding were measured postmortem in the dorsal and ventral striatum. RESULTS: Rats deemed socially dominant showed enhanced novelty reactivity but were neither more impulsive nor anxious compared with subordinate rats. Dominant rats additionally maintained higher rates of cocaine self-administration but showed no differences in the acquisition, extinction and reinstatement of this behaviour. D2/3 binding was elevated in the nucleus accumbens shell and dorsal striatum of dominant rats when compared to subordinate rats, and was accompanied by elevated DAT and reduced dopamine content in the nucleus accumbens shell. CONCLUSIONS: These findings show that social hierarchy influences the rate of self-administered cocaine but not anxiety or impulsivity in rats. Similar to non-human primates, these effects may be mediated by striatal dopaminergic systems.



Anxiety, High responder, Impulsivity, Psychostimulants, Resource competition, Social status, Animals, Behavior, Addictive, Cocaine, Corpus Striatum, Dopamine, Dopamine Plasma Membrane Transport Proteins, Dopamine Uptake Inhibitors, Exploratory Behavior, Male, Protein Binding, Rats, Receptors, Dopamine D2, Receptors, Dopamine D3, Reinforcement, Psychology, Self Administration, Social Dominance

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Psychopharmacology (Berl)

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Springer Science and Business Media LLC
Medical Research Council (G0001354)
Medical Research Council (G0701500)
Medical Research Council (G1000183)
Wellcome Trust (093875/Z/10/Z)
This research was supported by a Medical Research Council (MRC) grant to JWD (G0701500) and by a joint award from the MRC (G1000183) and Wellcome Trust (093875/Z/10/Z) in support of the Behavioural and Clinical Neuroscience Institute. The authors acknowledge additional funding from the MRC Imperial College – Cambridge University – Manchester University (ICCAM) strategic addiction cluster. BJ was supported by a Fellowship from the AXA Research Fund. ERJ was the recipient of a studentship from the Gates Foundation.