Stress, especially if psychological and uncontrollable, favors the development and aggravation of depression. In rodents repeated social defeat could be equivalent to loss of control and has been shown to induce behavioral and physiological changes that resemble some symptoms of depression. Consequently, repeated social defeat has been proposed as a model for depression and the study of underlying mechanisms and changes induced could yield inside into the etiology of human depression. In the present study we used in vivo microdialysis in subordinate rats to investigate extracellular levels of monoamines in prefrontal cortex and hippocampus under the influence of psychosocial stress. Rats followed a resident-intruder protocol for four consecutive days, during which physiological parameters were monitored (see SfN poster Ahnaou et al 2005). On day five, rats had visual, acoustic and olfactory, but no physical contact to dominant rats. This situation dissociates physical defeat stress from psychosocial stress...