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Cocaine Runs 'Round the Brain After the High

One dose triggers dopamine, addiction in mice

WEDNESDAY, May 30, 2001 (HealthDayNews) -- Snorting just a few lines of cocaine may trigger the part of your brain that influences addiction over the long run, a study in mice suggests.

"We speculate that it is possible that you open a window of vulnerability to addiction with just one dose of cocaine," says author Dr. Antonello Bonci, an assistant professor of neurology at the University of California, San Francisco. "And we know that this result can be generalized to humans, given the similarities between the neural system that is involved between humans and small mammals."

Bonci says a dose of cocaine can prime brain cells to respond to dopamine, the brain chemical that causes cravings. He says he discovered two years ago that the priming process, called long-term potentiation, is "a functional mechanism of the brain used to store memory as a way of learning." He says long-term potentiation, in which linked brain cells act at the same time and become more strongly connected, may be the basis of some kinds of memory and a first step towards dependence.

"Basically what we found was that a single injection of cocaine in mice, which would be more than a couple of lines of cocaine in humans, produces this long-term potentiation, Bonci says. "What happens is that a single dose releases more dopamine all over the brain, especially in the part of the brain strongly involved in addiction. The increased activity within the dopamine neurons lasts for five to seven days. And while the acute pleasurable effects of cocaine last but a few hours, this functional change of activity in the brain lasts for almost a week."

The findings were published in a letter in the May 31 issue of Nature.

Bonci says researchers don't yet know if the chemical and functional changes are permanent, "but it is certain that each time you take cocaine, you may be opening another window over and over again. The underlying effect may last much longer, but we just don't know yet."

The Drug Enforcement Administration (DEA) estimates that 3.7 million Americans took cocaine in 1999, 1.5 million regularly. While overall use has not gone up, the number of first-time users increased 63 percent between 1991 and 1998, from 574,000 to 934,000, the DEA reports. Cocaine use peaked in 1982, when 10.4 million Americans said they took cocaine, the agency says.

"This research has two bits of significance," says Alan Leshner, director of the National Institute on Drug Abuse (NIDA). "This shows that even a single drug use can have long-lasting chemical effects on the brain, and the nature of those changes tells you that there is no such thing anymore as recreational drug use."

"What's exciting about this research is that [it shows] one of the mechanisms by which drug use lays down the memory traces by which drug addiction occurs," Leshner says.

Five years ago, no one understood the role of memory and learning in drug addiction, Leshner says.

"The importance of learning and memory as a part of addiction is really only starting to be explored. What this piece of research is giving you is the brain mechanism of learning and memory's role in addiction," he says.

What To Do

The NIDA has more about cocaine. If you or someone you care about has a cocaine problem, check Cocaine Anonymous World Services.

Read these previous HealthDay articles about cocaine.

SOURCES: Interviews with Antonello Bonci, M.D., assistant professor of neurology, University of California, San Francisco, and Alan Leshner, Ph.D., director, NIDA, Bethesda, Md.; May 31, 2001, Nature
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