October 16, 2013
‘Hunger Hormone’ Ghrelin May Prevent PTSD, Say MIT Researchers
Michael Harper or redOrbit.com - Your Universe Online
Researchers from the Massachusetts Institute of Technology (MIT) say drugs created to suppress appetite may also be effective in preventing post-traumatic stress disorder (PTSD). At the heart of the research is ghrelin, what many refer to as the “hunger hormone.”When this hormone was found to trigger appetite in humans, many drug manufacturers set about creating drugs to block the biochemical as a way to prevent obesity. Yet as MIT researchers kept digging to better understand ghrelin, they found that it’s not just responsible for triggering hunger: it’s also released during bouts of chronic stress.
Now, researchers suggest that if military troops are given a dose of ghrelin as they go into battle, they may be able to better protect themselves against the risk of PTSD. The new research paper, written by assistant professor of brain and cognitive sciences Ki Goosens and recent graduate Retsina Meyer also claims ghrelin stimulates the secretion of a growth hormone but does not work in the same way as other stress hormones.
Their paper is published in the online journal Molecular Psychiatry.
Goosens says their research is particularly exciting because no drug is currently being issued to prevent PTSD.
When experienced in normal conditions, stress is not completely harmful. When stress becomes chronic, however, it can lead to anxiety, depression and other mental illnesses. A recent study published in the journal BMJ Open, for instance, found that women who experienced several stressful moments in the middle of their lives were more likely to develop Alzheimer's.
It’s been previously understood that a part of the brain which causes humans to feel fear can also respond to chronic stress. Unlike any other section of the brain, the amygdala responds to common stress by releasing a particular growth hormone. Goosens and team now say ghrelin triggers the amygdala to release this hormone, which is made in the stomach and then spreads throughout the rest of the body.
To test the effects of this hormone, the MIT researchers fed lab rats with drugs that either stimulated the ghrelin receptor or which overloaded them with growth hormone over an extended period of time. These rats were then trained to be afraid of a particular sound played by the researchers in the laboratory. The tone, they say, was mostly innocuous but could freeze the rats with fear. The animals that were fed the ghrelin receptor drug and the growth hormone drug were more likely to freeze when they heard the sound, a reaction which the researchers say indicates fear.
When the researchers reversed the drug therapy and began blocking the rats’ receptors to ghrelin or the growth hormone, they were no longer so afraid of the tone. The rats reacted in the same way those who had endured traumatic experiences in their life do, said Goosens.
“When you have people with a history of stress who encounter a traumatic event, they are more likely to develop PTSD because that history of stress has altered something about their biology. They have an excessively strong memory of the traumatic event, and that is one of the things that drives their PTSD symptoms,” said assistant professor Goosens.
The researchers then wondered if ghrelin was also responsible for the “fight or flight” hormone which is triggered in moments where adrenaline runs high. This mechanism is triggered by a response in the adrenal glands in rats, but when animals with this gland removed were administered ghrelin, they still became frightened. This indicates that ghrelin and adrenaline act independently of one another, allowing researchers to develop stress therapies specifically designed to address ghrelin.