Study: hungry mice are happy mice

Unhappy and want to be happy? A new study says you should get hungry.

When our bodies notice we need more calories, levels of a hormone called ghrelin increase. Ghrelin is known to trigger hunger, but new research suggests this may be a side effect of its primary job as a stress-buster.

Researchers manipulated ghrelin levels in mice through a variety of methods, including prolonged calorie restriction, ghrelin injection and a genetic modification rendering the mice numb to ghrelin's effect.

Mice who had limited ghrelin activity seemed depressed. If pushed into deep water they made no effort to swim. When introduced to a maze, they clung to the entryway. And when placed with other mice, they tended to keep to themselves. (These behaviors were reversed when the mice were given a low-dose antidepressant commonly prescribed to humans.)

In contrast, mice with high levels of ghrelin swam energetically in deep water, looking for escape. They eagerly explored new environments. And they were much more social.

The researchers think that hunger-induced happiness is an adaptive measure. Getting food, especially in the wild, requires concentration, clear-headed perception and often cooperation.

Hunger is not the only stressor that causes ghrelin to rise. Social anxiety can stimulate it as well. When mice were exposed to an older "bully" mouse, ghrelin levels rose and stayed high for weeks.

Elevated ghrelin could be why some people overeat when under pressure. If the stress-induced snack is avoided, the research suggests, ghrelin levels will remain high and help us confront the stressor in a calm, effective way.
Editor: Gareth Dodd 

RESOURCE/SOURCE: http://news.xinhuanet.com/english/2008-07/15/content_8550278.htm on Tuesday, July 15, 2008.