Pharmacological Resistance of Stress Enhanced Fear Learning in an Animal Model of Post-Traumatic Stress Disorder

Abstract

Pharmacological Resistance of Stress Enhanced Fear Learning in an Animal Model of Post-Traumatic Stress Disorder Virginia Long, Wendy Fujioka, Dorsa Amir and Michael Fanselow University of California, Los Angeles USA 1. Introduction In anxiety disorders such as PTSD, normal fear responding and learning, which is adaptive and helps us survive, is altered in such way that fear becomes maladaptive, interfering with an organism’s ability to alter and adapt behavior in situationally appropriate ways. Maladaptive fear learning is thought to underlie the behavioral symptoms of anxiety disorders such as PTSD (Charney, 2004; Rosen & Schulkin, 1998) when fear and fear responses dominate behavior even in benign circumstances. The fear learning circuit normally participates in adaptive learning and response to danger, however after trauma some individuals show symptoms of PTSD such as: abnormal response to milder stressors, increased vigilance and startle response (American Psychiatric Association., 2000). Stress enhanced fear learning (SEFL) models some specific aspects of PTSD. Using this model we can examine the consequences of trauma--how acute stress or a traumatic event permanently alters the way fear is learned and how these permanent changes in the fear learning circuitry produce maladaptive responses and maladaptive fear learning. Post-traumatic stress disorder (PTSD) is an anxiety disorder that is debilitating and profoundly affects the lives of men and women worldwide. The Diagnostic and Statistical Manual of Mental Disorders (DSM) criterion for a diagnosis of PTSD requires exposure or experience of a traumatic or life-threatening event (American Psychiatric Association., 2000). Trauma may be caused by combat, violence (such as assault, rape, robbery), severe accidents, disasters (natural or man-made). Any one of these traumatic events will be experienced by one-third of the population (Brunello et al., 2001). While the majority of people will not develop PTSD, it is estimated that 10 to 20% of people who experience an acute traumatic event will develop the disorder (Brunello et al., 2001). Symptoms of PTSD include re-experiencing of the trauma, avoidance, and hyper-arousal. Re-experiencing of the trauma can manifest as vivid and emotionally intense memories of the event in flashbacks, nightmares, or ruminations that give the patient a feeling of re-living the trauma. Avoidance of situations, people, or places that remind patients of the trauma is another aspect of the disorder. Increased physiological and psychological arousal, including enhanced startle response and hyper-vigilance also contribute and are indicative of the maladaptive fear learning associated with PTSD. PTSD is thought to be much more prevalent than the estimated 7.8%. Furthermore, many cases of PTSD may be unreported and thus undiagnosed (Brunello et al., 2001). www.intechopen.com