Rats as Addicts

Rats can emulate key signs of drug addiction in humans, according to two European studies that provide a basis for investigating important questions about addiction. Although researchers have been able to train rodents to repeatedly seek out drugs, it has been difficult to show that this behavior actually represents the compulsive behavior of a human addict. As a related "Perspective" notes, these studies beg such questions as why only some individuals switch from casual to compulsive drug use.

Véronique Deroche-Gamonet and colleagues in France found that rats trained to self-administer cocaine showed three of the essential behaviors of human addicts: difficulty stopping or limiting drug use, extremely high motivation to take the drug, and continued use despite harmful consequences. Approximately 17 percent of the rats in the study showed all three behaviors, which is similar to the proportion of human cocaine users that get diagnosed as addicts, according to the researchers. They suggest that addiction arises from interaction between two factors, the degree of exposure to drugs (which they say has been the focus of lab research) and a higher vulnerability to drugs in certain individuals (the focus of clinical studies).

In a second study, U.K. researchers Louk J. M. J. Vanderschuren and Barry J. Everitt showed that rats that had been self-administering cocaine for extended periods of time continued to do so even when they received an unpleasant shock. Rats that took the drug for less time stopped once the shocks began, although both groups sought roughly the same amounts of cocaine. These findings suggest that the first group of rats was showing compulsive behavior rather than a need for larger amounts of the drug, the authors say.

12 August 2004