Abstract: Hyperarousal represents the core symptoms of posttraumatic stress disorder (PTSD) and plays a significant role in the development of PTSD. Peri-traumatic hyperarousal response predicts the occurrence of the PTSD symptoms like re-experience, avoidance and numbing, and attenuating the magnitude of the arousal response during peri-traumatic period can reduce the risk to develop PTSD symptom. Dysfunction of hypothalamic–pituitary–adrenal axis characterized with over-release of norepinephrine (NE) and corticotropin-releasing factor (CRF), but lack of cortisol or corticosterone is one of the most important neural mechanisms which cause and maintain the long-term hyperarousal state. Over-activation of serotonin (5-HT) system is also related to the hyperarousal situation after the traumatic experience. Recently, the role of orexin system in hypothalamus in hyperaroual or stress has attracted a lot of attention, because the orexin system is closely connected with NE, CRF and 5-HT system and it is vital in sleep and arousal transition.

Key words: posttraumatic stress disorder, hyperarousal, orexin