WASHINGTON, Oct 29 (Reuters) Giving the body's natural appetite suppressant to morbidly obese volunteers de-activated their brain's response to tasty food -- and the new brain activity lasted for as long as the hormone was delivered, US researchers reported on Monday.
They said their imaging tests show some of the brain circuits activated by leptin, a hormone that helps control appetite, and may lead to new and better treatments for obesity, the researchers wrote in their report, published in the Proceedings of the National Academy of Sciences.
''While they were off leptin they got really hungry when they saw pictures of high-calorie food, and that was associated with high activation in a part of the brain that is related to food craving,'' said Edythe London of the University of California Los Angeles, who led the study.
With leptin, the executive centers involved in self-control were more activated. ''The findings suggest that leptin strengthens the executive centers,'' London said in a telephone interview.
The discovery of leptin in the 1990s created a furor, because when injected into rodents it caused them to eat less and lose weight. But the same rarely occurs in humans.
So experts are trying to find out how it works in people and find ways to better harness its effects.
London and colleagues examined three members of a family with a rare genetic defect that causes their bodies to produce no leptin.
Such people become extremely obese.
Earlier studies had shown that when injected with leptin, these people lose up to 50 percent of their body weight -- unlike most people, who usually continue to over-eat even when injected with leptin.
London wanted to see what was going on in their brains.
''In 2005 we found that leptin actually changes the structure of their brain,'' London said in a telephone interview. They found the area of the cerebral cortex involved in self-control actually grew after repeated leptin administrations.
But they wondered what else was going on.
They set up an experiment using functional magnetic resonance imaging, a type of brain scan that can see the brain's activity in real time. They recorded the brain activity before and after giving leptin, a study that continued for two years.
Pictures of food treats got the brain busy.
But different areas of the brain lit up with and without leptin, they reported.
One surprise was the activation of the cerebellum -- a section of the brain at the base of the head.
''Although the cerebellum has not traditionally been linked with eating behavior, it is thought to play a role in reinforcement and drug craving,'' they wrote.
''With leptin supplementation, the cerebellum showed enhanced activation,'' they wrote.
London said she is not sure what to make of this.
REUTERS BJR PM0314