Alterations in other compartments of the HPA axis were also identified in PTSD patients such as enhanced GR sensitivity and HPA axis enhanced negative feedback (Grossman et al., 2003; Duval et al., 2004; Yehuda et al., 2004b; Rohleder and Karl, 2006), elevated levels of CRH in the cerebrospinal fluid (Bremner et al., 1997; Baker et al., 1999) and reduced release of ACTH after CRH (Smith et al., 1989) and CCK4 (Kellner et al., 2000) administration. This evidence concerns the gene CRH and post-traumatic stress disorder.