High blood levels of a stress hormone called PACAP may explain why women but not men have a much higher risk of developing post-traumatic stress disorder (PTSD), according to a new US study published online in Nature this week.
The researchers, from Emory University and the University of Vermont, also found that women with a certain "protective" variation of the gene that codes for the PACAP hormone's receptor had a lower rate of PTSD than men, even though they had experienced similar levels of trauma.
The identification of PACAP (short for pituitary adenylate cyclase-activating polypeptide), as an indicator of PTSD could lead to new ways of diagnosing, and one day treating, anxiety disorders.
First author Dr Kerry Ressler, associate professor of psychiatry and behavioral sciences at Emory University School of Medicine in Atlanta, told the press their findings reveal a "new window" into the biology of PTSD.
"Few biological markers have been available for PTSD or for psychiatric diseases in general," said Ressler, who is also a researcher at the Yerkes National Primate Research Center.
We already know that PACAP broadly regulates the stress response at the cellular level: it acts throughout the body and the brain, influencing the central nervous system, immune function, blood pressure, metabolism, and sensitivity to pain.
But, as the authors wrote in their background information, it is not clear if the biological pathway that PACAP operates with its receptor, PAC1, has a role in human psychological stress responses, such as PTSD.
For their study, Ressler and colleagues, used data from the Grady Trauma Project, which included more than 1,200 low-income residents of Atlanta who experienced high levels of violence, physical and sexual abuse, resulting in high rates of PTSD for a civilian population.
Ressler, who is also a Howard Hughes Medical Institute Investigator, co-directs the Project with co-author Dr Bekh Bradley, an assistant professor of psychiatry and behavioral sciences at Emory and director of the Trauma Recovery Program at the Atlanta Veterans Affairs Medical Center.
The participants were patients who were attending the Grady Memorial Hospital in Atlanta. Starting in 2005, the researchers interviewed them in waiting rooms in the hospital's various primary care, ob-gyn and other clinics, and asked them to complete questionnaires about their life history, and give samples of blood and saliva.
The data showed that women, but not men, with high blood levels of PACAP showed more PTSD symptoms, such as finding it difficult to tell the difference between fear and safety signals, and being easily startled.