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Ghrelin, a chemical released in the brain after a stressful traumatic event might high up a person's chance of developing posttraumatic stress disorder, according to a new study. 

"Stress is a useful response to dangerous situations because it provokes action to escape or fight back," according to the study. "However, when stress is chronic, it can produce anxiety, depression and other mental illnesses," such as PTSD. 

"PTSD affects about 7.7 million American adults, including soldiers and victims of crimes, accidents, or natural disasters," states the Massachusetts Institute of Technology. "About 40 to 50 percent of patients recover within five years, Meyer says, but the rest never get better."

Ki Goosens, an assistant professor of brain and cognitive sciences at MIT, and senior author of the research paper suggests that medical providers could give active military members who are going to be deployed to a combat zone a ghrelin vaccine before leaving, lowering their chances of developing PTSD.

"That's exciting because right now there's nothing given to people to prevent PTSD," said Goosens.

According to Goosens, the brain structure that causes fear is the amygdala which has a unique response to chronic stress. "The amygdala produces large amounts of growth hormone during stress, a change that seems not to occur in other brain regions," said Goosens.

Goosens and her fellow researchers found that, "the release of the growth hormone in the amygdala is controlled by ghrelin, which is produced primarily in the stomach and travels throughout the body, including the brain."

Ghrelin levels are increased by chronic stress.

The researchers used rats to investigate how ghrelin levels impacted their reaction to stressful events. 

Researchers found that when the rats were treated with a drug used to trigger the ghrelin receptor over a long period of time, they were more vulnerable to fear than normal rats. 

"Fear was measured by training all of the rats to fear an innocuous, novel tone," according to the study. "While all rats learned to fear the tone, the rats with prolonged increased activity of the ghrelin receptor or overexpression of growth hormone were the most fearful, assessed by how long they froze after hearing the tone." 

Researchers said that in preventing the interaction of ghrelin with the cell receptors and the growth hormone it reduced the fear to normalize in chronically stressed rats.

"When rats were exposed to chronic stress over a prolonged period, their circulating ghrelin and amygdalar growth hormone levels also went up, and fearful memories were encoded more strongly," states the study. "This is similar to what the researchers believe happens in people who suffer from PTSD."
Researchers believe that one of the reasons why people are more prone to developing PTSD after a stressful event is because of the reoccurring appearance of ghrelin levels.

"So, could you immediately reverse PTSD? Maybe not, but maybe the ghrelin could get damped down and these people could go through cognitive behavioral therapy, and over time, maybe we can reverse it," said Retsina Meyer, lead author of the paper and a recent MIT PhD recipient.

The findings are published in the journal Molecular Psychiatry.