Researchers at the University of South Florida and the James A. Haley Veterans' Hospital in Tampa have developed new ways of assessing Post-Traumatic Stress Disorder (PTSD). These new studies show that strong, purely psychological stress produces behavioral symptoms in animal models similar to those commonly observed in people diagnosed with PTSD.
The investigators found that test rats exposed to two intense periods of stress, in conjunction with daily social stress, exhibited increased anxiety, heightened cardiovascular activity and impaired memory.
Phillip Zoladz, a USF doctoral student in psychology, conducted the research under the guidance of David Diamond, a research scientist with the Tampa VA and a professor of psychology and pharmacology at USF.
"Rats were exposed to a cat for one hour," Zoladz said. "No physical harm came to the rats because of a barrier between the rats and cat."
Diamond and Zoladz reasoned that because rats have a powerful instinctual fear of cats, the inability of the rats to escape from the cat would be traumatic, and that the experience would be analogous to the terror that people feel in life-threatening situations.
The rats were forced to "relive" their traumatic experience when they were unexpectedly exposed to the cat a second time, 10 days after the first exposure. Researchers also took into account the finding that a lack of social support can increase the likelihood that traumatized people will develop PTSD. The rats were housed with different cage mates on a daily basis to disrupt their social behaviors, followed by behavioral testing three weeks after the second exposure to cats.
People who experience horrific, life-threatening trauma, such as when soldiers are exposed to wartime combat, are at a substantial risk for developing post-traumatic stress disorder (PTSD). PTSD victims typically suffer from post-trauma distress because they relive their trauma through frequent flashback memories of the experience.
The USF and VA investigators suggested that this research can serve as a tool to develop pharmacological treatments which may alleviate the symptoms of PTSD in people.
"A substantial number of troops returning from the war in Iraq have been diagnosed with PTSD, according to the latest studies conducted by the U.S. Army," said Diamond. "As a result, there's an urgent need for research into the biological basis of PTSD to facilitate the development of treatments for this disorder."
Just as veterans of combat with PTSD have heightened anxiety that may persist long after they return to civilian life, rats displayed high levels of anxiety, an exaggerated response to being startled, and increased blood pressure long after they were exposed to the cat, explained Diamond. The cat-exposed rats also exhibited PTSD-like behavioral responses when they were given yohimbine, a drug that causes panic in people with PTSD. Importantly, the stressed rats exhibited profound memory deficits, which indicates they had impaired functioning of the hippocampus, a brain structure which is necessary for learning and memory and shows impaired functioning in people with PTSD.
"The animal model of PTSD is unique because it utilizes purely psychological forms of stress to produce long-lasting PTSD-like symptoms in rats," said Zoladz. "An advantage of this animal model of PTSD is that it will enable researchers to examine mechanisms in the brain that may be responsible for the pathological effects of traumatic stress on people."