Washington - Why does eating feel so good? The secret may lie in the head, not in the stomach, U.S. researchers reported on Thursday.

Tests on rats show that the appetite hormone ghrelin acts on pleasure receptors in the brain.

The findings may help researchers develop better diet drugs.

"In mice and rats ghrelin triggers the same neurons as delicious food, sexual experience, and many recreational drugs; that is, neurons that provide the sensation of pleasure and the expectation of reward," the researchers write in Friday's issue of the Journal of Clinical Investigation.

"These neurons produce dopamine and are located in a region of the brain known as the ventral tegmental area (VTA)," wrote the researchers, headed by Dr. Tamas Horvath of the Yale University School of Medicine in Connecticut.

Horvath's team found that ghrelin, itself only discovered in the last decade, acts on a molecular structure on brain cells called the ghrelin receptor growth hormone secretagogue 1 receptor or GHSR for short.

When ghrelin was infused into this area of the rats' brains, they ate as hungrily as they did after being kept hungry overnight, the researchers said.

Ghrelin is produced in the gut and triggers the brain to promote eating.

Several hormones are known to be involved in eating and appetite, and studies have shown that influencing them can affect weight gain in rats and mice. Influencing human eating behavior has proven far more difficult, however.

Horvath said it might be possible to design a drug that interferes with GHSR and thus help people with eating disorders.