As a consequence of social defeat, the intruder male displays subordinate posturing to prevent further attack from the resident male rat. During social defeat an aggressive resident male rat fights off an intruding male which has entered his territory. Social defeat is an ethologically relevant stressor which utilizes the natural establishment of social rank in male rodents. Currently, rodent models of PTSD encompass the use of acute or repeated stressors such as immobilization, forced swim ( Khan et al., 2004), underwater trauma, predator exposure ( Cohen et al., 2004), or inescapable foot shock ( Garrick, Morrow, Shalev, & Eth, 2001). Instead, behavioral testing in animal models of traumatic stress can measure physiological and behavioral endophenotypes associated with PTSD ( Cohen et al., 2004 Khan & Liberzon, 2004). In addition, behavioral tests in animal models of anxiety-like behavior cannot directly measure psychological symptoms such as flashbacks and nightmares ( Miller et al., 2006). The complexity of mood disorders like PTSD, however, makes the development of an appropriate animal model for PTSD challenging. The individual genetic or epigenetic and environmental characteristics of susceptibility to this disorder are not yet clear.Īnimal models of traumatic stress are being characterized for behavioral responses which may resemble aspects of PTSD ( Lister, 1990 Miller et al., 2006 Yehuda, Flory, Southwick, & Charney, 2006). A major feature of this condition is intrusive memories of the traumatic event that are often triggered by sensory input ( van der Kolk, 2006). PTSD is a mood disorder that can occur following repeated or extreme physical or psychosocial stress ( Miller & McEwen, 2006 Yehuda, McFarlane, & Shalev, 1998) and most likely interacts with an existing genetic liability ( Wakizono et al., 2007 Yehuda & Antelman, 1993). Severe psychosocial stressors can precipitate the development of mood disorders such as post traumatic stress disorder (PTSD). These data indicate that the severe stress of social defeat can produce physiologic and behavioral outcomes which may reflect aspects of traumatic psychosocial stress. Socially defeated rats displayed weight loss and an enhanced and prolonged response to acoustic startle which was displayed for up to 10 days following repeated social defeat. The objective of this study was to determine if behaviors elicited following repeated social defeat can also reflect aspects of ethologically relevant stresses associated with existing post traumatic stress disorder (PTSD) models. The social defeat model has been characterized to model aspects of the physiology and behavior associated with anxiety and depression. These effects of psychological or traumatic stressors may be mimicked in rats using the resident-intruder model of social defeat. Individuals exposed to psychological stressors may experience a long-term resetting of behavioral and neuroendocrine aspects of their “stress response” so that they either hyper or hypo-respond to subsequent stressors.
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