Researchers uncover more clues to causes of addiction


by Kathlyn Stone

November, 2007

Dozens of studies presented at the Society for Neuroscience annual meeting offered new, albeit preliminary, insights into the cause of addiction and possibilities for treatment. Among the findings reported: an old drug may offer a new answer for addiction treatment, sugar and cocaine might release similar brain chemicals, and the combination of two common addiction habits spells double trouble for learning and memory.

Scientists at the U.S. Department of Energy's Brookhaven National Laboratory focused on drug addicts’ cravings. Working with mice, they found that an antibiotic called D-cycloserine could reduce or eliminate drug addicts’ cravings.

D-cycloserine had previously been taken “off-label”—used in a way not originally intended—to successfully treat the fear of heights and other behavioral disorders. Researchers hypothesized that D-cycloserine might also change brain mechanisms related to addiction. In the Brookhaven study, mice that were given D-cycloserine were less likely than mice not treated with the drug to return to a space where they had been trained to expect cocaine.

Carlos Bermeo, a graduate student at the State University of New York at Stony Brook who was involved with the study, said D-cycloserine might turn out to be a plausible addiction treatment. "Since the association between drugs and the places where they are used can trigger craving or relapse in humans, a medication that could aid in the reduction or even extinction of such responses could be a powerful tool in the treatment of addiction," Bermeo said.

Another research group examined how rats would choose between competing cravings.

When given a choice between cocaine and water sweetened with saccharin, rats in a study conducted by French researchers gave new meaning to the term “sugar addict.”

The rats were housed in cages containing two levers. One dispensed an intravenous dose of cocaine and the other a drink of sweetened water. After two weeks, 40 of 43 rats repeatedly showed a preference for saccharin over cocaine.

In another study, the researchers tested 24 rats already addicted to cocaine. Over a 10-day period, a majority of the rats switched to the saccharin solution.

"Intense sweetness is more rewarding to the rats than cocaine," said Magalie Lenoir of the French National Center for Scientific Research in Bordeaux. Lenoir believes that excess sugar might increase dopamine levels in the brain, like cocaine does. The cravings for sugar or cocaine could just be a craving for the release of dopamine, she said.

Meanwhile, researchers at Temple University found that nicotine and alcohol, when used together, are more dangerous than previously thought. In mice, the combined use of the two drugs harmed animals’ ability to learn and remember by interfering with processes in the hippocampus, where new memories are formed.

"We wanted to see if nicotine and alcohol are interacting in the hippocampus or at another level, and what processes within the brain are they interacting with," said researcher Thomas J. Gould, an associate professor of psychology at Temple’s Center for Substance Abuse Research. Knowing where brain changes occur will give scientists a target for preventing symptoms of withdrawal.

The Temple study showed that nicotine might initially relieve cognitive losses associated with alcohol use but that a tolerance to nicotine developed with continued use. "We also found that a low dose of alcohol reverses nicotine withdrawal–associated deficits in learning,” Gould said. “Furthermore, we found that chronic nicotine produces cross-tolerance to the effects of a low dose of alcohol on learning."

In other words, if someone is addicted to both nicotine and alcohol, when they try to quit one addiction, the withdrawal they experience weakens both their ability to learn and their chances for beating the addiction, Gould said.