dysregulation. Differences in stress hormone levels can influence moods due to the negative effect of high cortisol concentrations on biochemicals that regular mood such as serotonin. Research has found that people with MDD have elevated cortisol levels in response to stress and that low serotonin levels are related to the development of depression. Thus, it is possible that a dysregulation in the HPA, when combined with the increased history of traumatic events, may contribute to the gender differences seen in depression. Coping mechanisms in PTSD For PTSD, genders differences in coping mechanisms has been proposed as a potential explanation for observed gender differences in PTSD prevalence rates. Though PTSD is a common diagnosis associated with abuse and trauma for men and women, the "most common mental health problem for women who are trauma survivors is depression". Studies have found that women tend to respond differently to stressful situations than men. For example, men are more likely than women to react using the fight-or-flight response. Additionally, men are more likely to use problem-focused coping, which is known to decrease the risk of developing PTSD when a stressor is perceived to be within an individual's control. Women, meanwhile, are thought to use emotion-focused, defensive, and palliative coping strategies. As well, women are more likely to engage in strategies such as wishful thinking, mental disengagement, and the suppression of traumatic memories. These coping strategies have been found in research to correlate with an increased likelihood of developing PTSD. Women are more likely to blame themselves following a traumatic event than men, which has been found to increase an individual's risk of PTSD. In addition, women have been found to be more sensitive to a loss of social support following a traumatic event than men. A variety of differences in coping mechanisms and use of coping mechanisms may likely play a role in observed gender differences in PTSD. These described differences in coping mechanisms are in line with a preliminary model of sex-specific pathways to PTSD. The model, proposed by Christiansen and Elklit, suggests that there are sex differences in the physiological stress response. In this model, variables such as dissociation, social support, and use of emotion-focused coping may be involved in the development and maintenance of PTSD in women, whereas physiological arousal, anxiety, avoidant coping, and use of problem-focused coping may be more likely to be related to the development and maintenance of