title: Social rank, chronic ethanol self-administration, and diurnal pituitary-adrenal activity in cynomolgus monkeys.
abstract: BACKGROUND
  Dominance hierarchies affect ethanol self-administration, with greater intake among subordinate animals compared to dominant animals. Excessive ethanol intake disrupts circadian rhythms. Diurnal rhythms of the hypothalamic-pituitary-adrenal axis have not been characterized in the context of ethanol self-administration with regard to social rank.
  
  
  OBJECTIVE
  This study aimed to determine whether diurnal pituitary-adrenal hormonal rhythms account for differences between social ranks in ethanol self-administration or are differentially affected by ethanol self-administration between social ranks.
  
  
  METHODS
  During alternating individual (n = 11-12) and social (n = 3 groups) housing of male cynomolgus monkeys (Macaca fascicularis), diurnal measures of cortisol and adrenocorticotropic hormone (ACTH) were obtained from plasma samples three times per week. Social rank was determined, ethanol (4 %, w/v) self-administration was induced, and then the monkeys were allowed a choice of water or ethanol for 22 h/day for 49 weeks.
  
  
  RESULTS
  For all social ranks, plasma ACTH was elevated during social housing, but cortisol was stable, although greater among dominant monkeys. Ethanol self-administration blunted the effect of social housing, cortisol, and the diurnal rhythm for both hormones, regardless of daily ethanol intake (1.2-4.2 g/kg/day). Peak ACTH and cortisol were more likely to be observed in the morning during ethanol access. Ethanol, not vehicle, intake was lower during social housing across social ranks. Only dominant monkeys showed significantly lower blood-ethanol concentration during social housing.
  
  
  CONCLUSIONS
  There was a low threshold for disruption of diurnal pituitary rhythms by ethanol drinking, but sustained adrenal corticosteroid rhythms. Protection against heavy drinking among dominant monkeys may have constrained ethanol intoxication, possibly to preserve dominance rank.
authors.affiliation: Oregon National Primate Research Center, Oregon Health and Science University, 505 NW 185th Avenue, Beaverton, OR 97006, USA. helmsc@ohsu.edu
authors.forename: Christa M
authors.initials: CM
authors.lastname: Helms
authors.forename: Megan N
authors.initials: MN
authors.lastname: McClintick
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Grant
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000097:blood; D000818:Animals; D002755:Choice Behavior; D002940:Circadian Rhythm / Q000187:drug effects*; D000431:Ethanol / Q000008:administration & dosage* / Q000097:blood; D006799:Housing, Animal; D006854:Hydrocortisone / Q000097:blood; D008252:Macaca fascicularis; D008297:Male; D010913:Pituitary-Adrenal System / Q000187:drug effects*; D012646:Self Administration; D012930:Social Dominance
chemical_list: D000431:Ethanol; D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone