Nicotine addiction curbed by new drug.

Given nicotine regularly, rats--like humans--can become addicted. A study of 60 such rats shows that an anti-epilepsy drug called gamma vinyl-GABA, or GVG, blocks the craving, scientists led by a team at Brookhaven National Laboratory in Upton, N.Y., report in the January SYNAPSE. A test on baboons unveils similar findings.

When rats getting 75 milligrams of GVG per kilogram of body weight were given access to a nicotine dispenser in their cages, they tapped the dispenser at their usual rate to satisfy their addiction. Rats getting 90 mg/kg, however, consumed only half as much nicotine. At higher doses, GVG abolished nicotine craving completely. A similar pattern resulted from tests on other rats conditioned to get nicotine from a dispenser in response to specific cues--a model of humans' urge to smoke in certain situations, such as while drinking alcohol or coffee.

The anti-epilepsy drug boosts production of gamma-aminobutyric acid. This brain chemical inhibits release of dopamine, a pleasure-inducing substance. Production of dopamine is triggered by nicotine, cocaine, alcohol, and some other drugs. Indeed, previous studies have indicated that GVG inhibits animals from sensing a reward from these drugs. "It looks like there might be a global, generalizable strategy to treat multiple addictions," says study coauthor Stephen L. Dewey, a neuroanatomist at Brookhaven.

The researchers used positron emission tomography to measure dopamine in the brains of baboons: seven that were undrugged, three that received nicotine only, four that were given GVG only, and six that received both. In the baboons, GVG blocked the dopamine release resulting from nicotine.

From these findings, the researchers estimate that the daily adult human dose of GVG needed for smoking cessation would be 250 to 500 mg, much less than the dose currently given to epilepsy patients to prevent seizures.