About a dozen years ago, scientists discovered that a hormone called ghrelin enhances appetite. Dubbed the “hunger hormone,” it was quickly targeted by drug companies seeking treatments for obesity—none of which have yet panned out.
MIT neuroscientists have now discovered that ghrelin’s role goes far beyond stimulating hunger. The researchers found that ghrelin released during chronic stress makes the brain more vulnerable to emotional trauma, suggesting that it may predispose people to post-traumatic stress disorder (PTSD). This means that drugs that reduce ghrelin levels could help protect people who are at high risk for PTSD, such as soldiers serving in war, says Ki Goosens, an assistant professor of brain and cognitive sciences at MIT and senior author of a paper describing the findings in the journal Molecular Psychiatry.
Stress is a useful response to dangerous situations because it provokes action to escape or fight back. However, when stress is chronic, it can produce anxiety, depression, and other mental illnesses. During stressful situations, the stomach increases its production of ghrelin, which travels throughout the body and boosts the release of growth hormone in the amygdala, a brain structure that plays a critical role in processing fear and other emotions.
Goosens and her colleagues stimulated ghrelin activity in rats over a prolonged period and found that they became much more susceptible to fear than normal rats. When different rats were exposed to long-term chronic stress, their levels of circulating ghrelin went up, and so did the levels of growth hormone in their amygdalas. Fearful memories induced in these rats were encoded more strongly. This is similar to what the researchers believe happens in people who suffer from PTSD, which affects about 7.7 million American adults, including soldiers and victims of crimes, accidents, or natural disasters.
People with a history of stress who encounter a traumatic event “are more likely to develop PTSD because that history of stress has altered something about their biology,” Goosens says.
The researchers believe that drugs that interfere with ghrelin could be given to people entering stressful situations—or even used to treat people who already suffer from PTSD, because ghrelin levels remain high long after the chronic stress ends.