Craving fat? Blame it on a brain protein.

If your favorite foods include items such as potato chips, fried chicken, and ice cream -- and if you find it nearly impossible to "eat just one" - the problem may literally be in your head, new research suggests.

A team of neuroscientists led by Sarah F. Leibowitz at Rockefeller University in New York City has uncovered evidence in rats that a brain protein called galanin dictates the craving for fatty foods. Moreover, the group has found that a drug that blocks galanin's activity can reduce an animal's appetite for fat.

Leibowitz described these results last week at the Society for Neuroscience's annual meeting in Anaheim, Calif. She and her colleagues studied the brains of rats that had been allowed over a threeweek period to eat as much as they wanted of three specially prepared foods: milk protein, a high-carbohydrate mixture of sugar and cornstarch, and lard.

Leibowitz's team found that rats with high natural concentrations of galanin in a brain region called the hypothalamus ate more lard each day and gained more weight over the study period than did rats with low galanin concentrations -- despite the fact that both groups consumed roughly the same amount of protein and carbohydrate each day. In addition, the researchers observed, the rats with high galanin levels almost always began their meals by lapping up lard, indicating that they might be trying to satisfy a craving.

In a second study reported at the conference, Leibowitz' group ruled out the possibility that the extra galanin might have arisen elsewhere in the rats' bodies and then traveled to their brains. The researchers discovered high concentrations of galanin messenger RNA (mRNA) -- the chemical intermeidary through which the galanin gene directs the production of galanin--in brain cells taken from overweight rats with a strong predilection for fat. They also found that these rats had reduced concentrations of insulin in the blood, indicating that galanin serves as a biochemical link between obesity and diabetes.

"Animals with high galanin levels have high fat intake," summarizes Leibowitz, "and these animals also have lower levels of insulin." However, she adds, her team has not yet determined how galanin and insulin interact.

"The data are quite interesting," comments Michael Schwartz of the Veterans Administration Medical Center in Seattle. But he cautions that Leibowitz's group needs to study rats fed only fat to make certain that the elevated galanin they observed is not simply the result of a high-fat diet. Until then, he contends, the researchers "don't know whether the galanin is causing the increased fat intake or if the increased fat intake is causing the increased galanin."

Leibowitz counters that earlier experiments by her group and others have shown that rats receiving galanin injections in a specific region of their hypothalamus eat much more fat than do control rats given galanin injections elsewhere in their brains. Moreover, she says, the galanin injections make the fat-gobbling rats sluggish, reducing their metabolism and leading to weight gain.

Leibowitz and her colleagues have recently found that an experimental drug called M40 can slash a rat's fat craving by blocking the activity of galanin in its hypothalamus. In the November/December BRAIN RESEARCH, she and Rockefeller colleague Taewan Kim report that rats given extra galanin to boost their fat intake resume eating normal amounts of fat following injections of M40.

Several drug companies are now developing compounds similar to M40. Leibowitz says she and her co-workers hope to begin clinical trials of M40 "within the next couple of years" among patients with eating disorders. She adds that the drug might also benefit diabetics who have difficulty controlling their weight.