title: Middle-range exploratory activity in adult rats suggests higher resilience to chronic social defeat.
abstract: OBJECTIVE
  Stressful life events play an important role in the aetiology of human mood disorders and are frequently modelled by chronic social defeat (SD) in rodents. Exploratory phenotype in rats is a stable trait that is likely related to inter-individual differences in reactivity to stress. The aim of the study was to confirm that low levels of exploratory activity (LE) are, in rodents, a risk factor for passive stress coping, and to clarify the role of medium (ME) and high (HE) exploratory disposition in the sensitivity to SD.
  
  
  METHODS
  We examined the effect of SD on male Wistar rats with LE, ME, and HE activity levels as measured in the exploration box. After SD, the rats were evaluated in social preference, elevated zero maze, and open-field tests. Brain tissue levels of monoamines were measured by high-performance liquid chromatography.
  
  
  RESULTS
  Rats submitted to SD exhibited lower weight gain, higher sucrose consumption, showed larger stress-induced hyperthermia, lower levels of homovanillic acid in the frontal cortex, and higher levels of noradrenaline in the amygdala and hippocampus. Open-field, elevated zero maze, and social preference tests revealed the interaction between stress and phenotype, as only LE-rats were further inhibited by SD. ME-rats exhibited the least reactivity to stress in terms of changes in body weight, stress-induced hyperthermia, and sucrose intake.
  
  
  CONCLUSIONS
  Both low and high novelty-related activity, especially the former, are associated with elevated sensitivity to social stress. This study shows that both tails of a behavioural dimension can produce stress-related vulnerability.
authors.affiliation: Department of Psychology,Estonian Centre of Behavioural and Health Sciences,Division of Neuropsychopharmacology,University of Tartu,Tartu,Estonia.
authors.forename: Denis
authors.initials: D
authors.lastname: Matrov
authors.affiliation: Department of Psychology,Estonian Centre of Behavioural and Health Sciences,Division of Neuropsychopharmacology,University of Tartu,Tartu,Estonia.
authors.forename: Kadri
authors.initials: K
authors.lastname: Kõiv
authors.affiliation: Department of Psychology,Estonian Centre of Behavioural and Health Sciences,Division of Neuropsychopharmacology,University of Tartu,Tartu,Estonia.
authors.forename: Margus
authors.initials: M
authors.lastname: Kanarik
authors.affiliation: Department of Psychology,Estonian Centre of Behavioural and Health Sciences,Division of Neuropsychopharmacology,University of Tartu,Tartu,Estonia.
authors.forename: Krista
authors.initials: K
authors.lastname: Peet
authors.affiliation: Department of Psychology,Estonian Centre of Behavioural and Health Sciences,Division of Neuropsychopharmacology,University of Tartu,Tartu,Estonia.
authors.forename: Karita
authors.initials: K
authors.lastname: Raudkivi
authors.affiliation: Department of Psychology,Estonian Centre of Behavioural and Health Sciences,Division of Neuropsychopharmacology,University of Tartu,Tartu,Estonia.
authors.forename: Jaanus
authors.initials: J
authors.lastname: Harro
mesh_terms: D000223:Adaptation, Psychological / Q000502:physiology; D000818:Animals; D015306:Biogenic Monoamines / Q000378:metabolism; D001923:Brain Chemistry; D002853:Chromatography, Liquid; D003866:Depressive Disorder / Q000378:metabolism / Q000503:physiopathology* / Q000523:psychology; D004195:Disease Models, Animal; D005106:Exploratory Behavior / Q000502:physiology*; D008297:Male; D018782:Maze Learning; D051381:Rats; D017208:Rats, Wistar; D012919:Social Behavior
chemical_list: D015306:Biogenic Monoamines
keywords: depression; exploratory behaviour; inter-individual differences; social defeat; vulnerability