A study of rats finds they show all the signs of addiction to sugar. The finding could help better understand eating disorders in humans.

Professor Bart Hoebel and his team in the Department of Psychology and the Princeton Neuroscience Institute have been studying signs of sugar addiction in rats for years. They had previously demonstrated a behavioral pattern of increased intake and then showed signs of withdrawal.

New experiments captured craving and relapse to complete the picture.

"If bingeing on sugar is really a form of addiction, there should be long-lasting effects in the brains of sugar addicts," Hoebel said. "Craving and relapse are critical components of addiction, and we have been able to demonstrate these behaviors in sugar-bingeing rats in a number of ways."

The findings are being reported this week at the annual meeting of the American College of Neuropsychopharmacology in Scottsdale, Ariz.,

"We have the first set of comprehensive studies showing the strong suggestion of sugar addiction in rats and a mechanism that might underlie it," Hoebel said.

Rats function much like humans in many ways, which is why they are used as test subjects.

Rats denied sugar for a prolonged period after learning to binge worked harder to get it when it was reintroduced. They consumed more sugar than they ever had before, suggesting craving and relapse behavior. Their motivation for sugar had grown.

"In this case, abstinence makes the heart grow fonder," Hoebel said.

The rats drank more alcohol than normal after their sugar supply was cut off, showing that the bingeing behavior had forged changes in brain function. These functions served as "gateways" to other paths of destructive behavior, such as increased alcohol intake, Hoebel's team figures.

Also, after receiving a dose of amphetamine normally so minimal it has no effect, they became significantly hyperactive. The increased sensitivity to the psychostimulant is a long-lasting brain effect that can be a component of addiction, Hoebel said.

More research is needed to understand the implications for people.

"It seems possible that the brain adaptations and behavioral signs seen in rats may occur in some individuals with binge-eating disorder or bulimia," Hoebel said. "Our work provides links between the traditionally defined substance-use disorders, such as drug addiction, and the development of abnormal desires for natural substances. This knowledge might help us to devise new ways of diagnosing and treating addictions in people."