title: Social dominance in rats: effects on cocaine self-administration, novelty reactivity and dopamine receptor binding and content in the striatum.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
authors.affiliation: Department of Psychology, University of Cambridge, Downing Street, Cambridge, CB2 3EB, UK.|Behavioural and Clinical Neurosciences Institute, University of Cambridge, Cambridge, CB2 3EB, UK.
authors.forename: Bianca
authors.initials: B
authors.lastname: Jupp
authors.affiliation: Department of Psychology, University of Cambridge, Downing Street, Cambridge, CB2 3EB, UK.|Behavioural and Clinical Neurosciences Institute, University of Cambridge, Cambridge, CB2 3EB, UK.
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Murray
authors.affiliation: Department of Psychology, University of Cambridge, Downing Street, Cambridge, CB2 3EB, UK.|Behavioural and Clinical Neurosciences Institute, University of Cambridge, Cambridge, CB2 3EB, UK.
authors.forename: Emily R
authors.initials: ER
authors.lastname: Jordan
authors.affiliation: Department of Psychology, University of Cambridge, Downing Street, Cambridge, CB2 3EB, UK.|Behavioural and Clinical Neurosciences Institute, University of Cambridge, Cambridge, CB2 3EB, UK.
authors.forename: Jing
authors.initials: J
authors.lastname: Xia
authors.affiliation: Department of Psychology, University of Cambridge, Downing Street, Cambridge, CB2 3EB, UK.|Behavioural and Clinical Neurosciences Institute, University of Cambridge, Cambridge, CB2 3EB, UK.
authors.forename: Meg
authors.initials: M
authors.lastname: Fluharty
authors.affiliation: Molecular Imagine Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, USA.
authors.forename: Saurav
authors.initials: S
authors.lastname: Shrestha
authors.affiliation: Department of Psychology, University of Cambridge, Downing Street, Cambridge, CB2 3EB, UK.|Behavioural and Clinical Neurosciences Institute, University of Cambridge, Cambridge, CB2 3EB, UK.
authors.forename: Trevor W
authors.initials: TW
authors.lastname: Robbins
authors.affiliation: Department of Psychology, University of Cambridge, Downing Street, Cambridge, CB2 3EB, UK. jwd20@cam.ac.uk.|Behavioural and Clinical Neurosciences Institute, University of Cambridge, Cambridge, CB2 3EB, UK. jwd20@cam.ac.uk.|Department of Psychiatry, University of Cambridge, Cambridge, CB2 2QQ, UK. jwd20@cam.ac.uk.
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Dalley
mesh_terms: D000818:Animals; D016739:Behavior, Addictive / Q000378:metabolism; D003042:Cocaine / Q000008:administration & dosage*; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism; D050483:Dopamine Plasma Membrane Transport Proteins / Q000378:metabolism; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology; D005106:Exploratory Behavior / Q000187:drug effects* / Q000502:physiology; D008297:Male; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D050637:Receptors, Dopamine D3 / Q000378:metabolism*; D012054:Reinforcement, Psychology; D012646:Self Administration; D012930:Social Dominance
chemical_list: D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D003042:Cocaine; D004298:Dopamine
keywords: Anxiety; High responder; Impulsivity; Psychostimulants; Resource competition; Social status