Rats can become addicts, studies show

By Lauran Neergaard
The Associated Press

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Scientists previously had proved that rats will take drugs, even eagerly. French and British research, published yesterday in the journal Science, shows they can become addicted.

The studies also could help scientists learn what makes some people particularly vulnerable to addiction and could lead to new anti-drug therapies, addiction specialists say.

"What confers susceptibility to experimenting and trying drugs may be quite different than what changes your brain and leads to addiction," said Terry Robinson, a University of Michigan neuroscientist. "These articles provide us the approaches and the techniques to ask the latter."

Among the ways to know when a rat is hooked: It tries to get cocaine even when each hit comes with an electric shock.

In the French study, rats poked their noses through holes in their cages to trigger injections of cocaine. They were allowed access to cocaine for three months, much longer than the 10- to 30-day drug-use studies normally done with animals.

Compulsive drug-seeking even in the face of bad consequences is a measure of human addiction. So researchers routinely cut off the drug supply and measured the rats' persistence, seeing how hard they worked to get the drug and noting whether they gave up when their feet were shocked.

Intriguingly, 17 percent of the rats met the measures and thus were considered addicted — while roughly 15 percent of human cocaine users become addicts, said lead researcher Pier Vincenzo Piazza of INSERM, France's National Institute of Health and Medical Research.

The British study focused only on the bad-consequences scenario. Rats who used cocaine for longer periods continued to do so even when their feet were shocked, said Louk Vanderschuren, who led the study at the University of Cambridge. But rats who had used cocaine for a short period quit after they knew the punishment.

Both studies concluded that extended exposure to cocaine is a key to addiction, but Piazza said that must be combined with some underlying genetic vulnerability — to explain why all rats didn't succumb.

"The huge question for the future, then, is what confers the susceptibility," Robinson said.

Copyright © 2004 The Seattle Times Company

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