The appetite-curbing hormone leptin influences brain circuits that tell us when we are hungry and when we are full, according to a study released Monday that could help in the fight against obesity.

Understanding how leptin alters brain functions gives an insight into how the hormone should operate normally, said researchers at the University of California at Los Angeles Semel Institute for Neuroscience and Human Behavior.

"Ultimately, that may help identify new targets for the treatment of obesity and related metabolic disorders," said Edythe London, a professor of psychiatry at UCLA's Semel Institute.

The team studied the brain activity in three morbidly obese people as they were presented with visual food cues using brain scanning technology known as functional magnetic resonance imaging, or fMRI.

The three volunteers were all members of a Turkish family who were overweight because of an extremely rare genetic mutation which resulted in them being deficient in leptin -- a signaling molecule produced by fat cells.

To see how leptin affected their relationship with food, the trio were shown images of food when they were supplemented with the hormone and again when they were not.

The cues included images of high-calorie food such as fried chicken, pizza and cheeseburgers, low-calorie food such as strawberries and salad, and neutral images such as brick walls.

Leptin treatment reduced feelings of hunger stimulated by the images. Artificial supplementation of leptin was also associated with reduced activity in brain regions associated with hunger, and increased activity in regions previously linked with feeling full or satisfied.

In clinical trials, leptin supplements have produced moderate weight loss in some obese patients, supposedly by inhibiting hunger and promote feelings of being full. But other research suggests it does not help people with normal leptin levels shed the extra pounds.

The study appears in the Proceedings of the National Academy of Sciences. (AFP) -CHICAGO, Oct 29, 2007


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