title: Social dominance in female monkeys: dopamine receptor function and cocaine reinforcement.
abstract: BACKGROUND
  Brain imaging and behavioral studies suggest an inverse relationship between dopamine (DA) D2/D3 receptors and vulnerability to cocaine abuse, although most research has used males. For example, male monkeys that become dominant in a social group have significant elevations in D2/D3 receptor availability and are less vulnerable to cocaine reinforcement.
  
  
  METHODS
  DA D2/D3 receptor availability was assessed in female cynomolgus monkeys (n = 16) with positron emission tomography (PET) while they were individually housed, 3 months after stable social hierarchies had formed, and again when individually housed. In addition, PET was used to examine changes in dopamine transporter (DAT) availability after social hierarchy formation. After imaging studies were complete, monkeys received implantation with indwelling intravenous catheters and self-administered cocaine (.001-.1 mg/kg/injection) under a fixed-ratio 30 schedule of reinforcement. Acquisition of cocaine reinforcement occurred when response rates were significantly higher than when saline was self-administered.
  
  
  RESULTS
  Neither DAT nor D2/D3 receptor availability in the caudate nucleus and putamen was predictive of social rank, but both significantly changed after formation of social hierarchies. DA D2/D3 receptor availability significantly increased in females that became dominant, whereas DAT availability decreased in subordinate females. Dominant female monkeys acquired cocaine reinforcement at significantly lower doses than subordinate monkeys.
  
  
  CONCLUSIONS
  The relationship between D2/D3 receptor availability and vulnerability to cocaine reinforcement seems, on the basis of these findings, opposite in females and males. These data indicate that the social environment profoundly affects the DA system but does so in ways that have different functional consequences for females than for males.
authors.affiliation: Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA. mnader@wakehealth.edu
authors.forename: Michael A
authors.initials: MA
authors.lastname: Nader
authors.forename: Susan H
authors.initials: SH
authors.lastname: Nader
authors.forename: Paul W
authors.initials: PW
authors.lastname: Czoty
authors.forename: Natallia V
authors.initials: NV
authors.lastname: Riddick
authors.forename: H Donald
authors.initials: HD
authors.lastname: Gage
authors.forename: Robert W
authors.initials: RW
authors.lastname: Gould
authors.forename: Brandi L
authors.initials: BL
authors.lastname: Blaylock
authors.forename: Jay R
authors.initials: JR
authors.lastname: Kaplan
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Garg
authors.forename: Huw M L
authors.initials: HM
authors.lastname: Davies
authors.forename: Daniel
authors.initials: D
authors.lastname: Morton
authors.forename: Sudha
authors.initials: S
authors.lastname: Garg
authors.forename: Beth A
authors.initials: BA
authors.lastname: Reboussin
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002421:Caudate Nucleus / Q000378:metabolism* / Q000503:physiopathology; D003042:Cocaine / Q000378:metabolism / Q000494:pharmacology*; D050483:Dopamine Plasma Membrane Transport Proteins / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D006719:Homovanillic Acid / Q000134:cerebrospinal fluid; D008252:Macaca fascicularis; D008597:Menstrual Cycle / Q000134:cerebrospinal fluid; D049268:Positron-Emission Tomography; D011699:Putamen / Q000378:metabolism* / Q000503:physiopathology; D011954:Receptors, Dopamine / Q000187:drug effects* / Q000378:metabolism; D012646:Self Administration; D012737:Sex Factors; D012930:Social Dominance
chemical_list: D050483:Dopamine Plasma Membrane Transport Proteins; D011954:Receptors, Dopamine; D003042:Cocaine; D006719:Homovanillic Acid