Ghrelin regulates hunger pangs
High levels of the "hunger hormone" ghrelin have an antidepressant effect, US researchers claim.
Blocking the body's response to ghrelin has been suggested as a weight loss treatment but it may also produce unintended effects on mood, they said.
The Nature Neuroscience study found mice with increased levels of the hormone showed fewer signs of depression and anxiety.
Experts said the idea was interesting but further studies were needed.
Ghrelin is released by the empty stomach into the bloodstream before moving to the brain, where it triggers feelings of hunger.
Treatment with the hormone itself - or a drug designed to cancel its effects - might be able to help both people who are eating too little, such as cancer patients, or those who eat too much, researchers believe.
In the latest study, Dr Jeffrey Zigman and colleagues restricted the food intake of laboratory mice for 10 days, causing their ghrelin levels to quadruple.
Compared with mice who had free access to food, the calorie-restricted mice showed lower levels of depression and anxiety when subjected to mazes and other behaviour tests.
The team also looked at mice genetically engineered to be unable to respond to ghrelin.
When they were fed a restricted-calorie diet they did not experience the antidepressant or anti-anxiety effects.
The researchers found the same thing when they induced higher ghrelin levels by subjecting the mice to stress.
Those mice that could not respond to ghrelin had greater levels of depression-like symptoms than the normal mice.
"Our findings in mice suggest that chronic stress causes ghrelin levels to go up, and that behaviours associated with depression and anxiety decrease when ghrelin levels rise," said Dr Zigman, a researcher at UT Southwestern Medical Center in Dallas.
"An unfortunate side effect, however, is increased food intake and body weight," he added.
He said the results made sense from an evolutionary standpoint, as hunter-gatherers may have had a survival advantage in remaining calm and collected in times of hunger in order for them to successfully find food.
The researchers are now hoping to look at the antidepressant effect of the hormone in conditions such as anorexia.
Professor Stephen Bloom, an expert in appetite regulation at Imperial College London, said it was reasonable to believe that ghrelin had an impact on behavioural responses other than just hunger.
But he said there was a lot of research to be done before it could be confirmed that a hormone released in the stomach can have an effect on mood in the brain.
"The role of ghrelin in the gut and in the brain are likely to be completely different," he said.