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Background: One of the major sources of stress in most species including humans is of a social nature. In humans social conflicts may originate sequelae of negative emotions eventually leading to isolation, anxiety and depression. The present experiments were based on the rat resident-intruder paradigm which is one of the better characterized animal models for social stress. The aim of the studies was to better understand how social stress experiences may determine persisting behavioural and physiological changes, relevant for the development and maintenance of symptoms related to human psychopathologies such as anxiety and depression. In the present study, the temporal dynamics of this social stress were examined, focusing on the long term conditioning properties of social defeat. Methods: Male Sprague-Dawley intruder rats were exposed to aggressive conspecific residents. During 3 daily 30 min encounters, intruders were either defeated or threatened by residents, providing the defeated-threatened (DT) and threatened-threatened (TT) groups respectively, or exposed to a novel empty cage (EC). The effect of such exposures on both behaviour and hypothalamo–pituitary–adrenal (HPA) axis parameters were assessed in 3 separate experiments 8, 14, or 21 days following the last session, by exposing subject animals to either a threatening resident (DT and TT groups) or to an empty cage (EC group) for 15 min. Results: A specific and persistent behavioural conditioning was observed for both socially defeated animals and animals exposed only to social threat, highlighting a lack of habituation for the conditioning properties of this social stressor. At all timepoints examined, spatial and social exploration were decreased in DT (p |
