Is the Secret to Curing Addiction in an Aquarium?
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Just as with humans, some rats found their habit harder to kick than others. When the scientists introduced a punishment alongside the stimulant—an electric shock, for example—many of the rats stopped indulging. But 20%-25% of them continued pressing the lever and getting their hit, even though they knew there was a big down side. They'd found their rat addicts.
And interestingly, just as in humans, two things could trigger a relapse: a small dose of the stimulant (how many ex-smokers have learned the reality behind the statement "Just one won't hurt"?), or a stressful incident, such as a pinching of the tail.
Zebrafish, tropical freshwater fish popular with aquarium keepers, have several advantages over rats. First, they have more offspring—the female produces hundreds of eggs in each clutch. Second, they're hardy, and can survive more genetic "meddling" than mammals. And finally, the fertilized eggs of the zebrafish are transparent, and develop in water, outside the mother's womb, which makes it easier to see what's going on from a developmental perspective. In fact, the science community is enjoying something of a love affair with the zebrafish, using it in research into areas as varied as cancer, genetics, neurobiology, teratology and stem cells.
But the crucial question for us, surely, is: Can fish get addicted? Well, fish can't press levers, so Dr. Parker and his team had to be a little more imaginative with their delivery system. But before long, they'd established that zebrafish, just like humans and rats, were partial to a wide range of stimulants.
There has been much debate about how much of the "addictive personality" is heritable and how much is down to environment. While the genetics involved are highly complex, Dr. Parker and company can now say with certainty that there is a large genetic component to addiction—for nicotine, at least—and have a much better idea about the specific genes involved.
Many theories had been circulating as to which personality traits are good indicators of a predilection to addiction, with candidates including neuroticism, extraversion, impulsivity (a tendency to act without thinking), novelty-seeking (a propensity to boredom, and the frequent desire for new and varied experiences), and risk-taking. But no one had ever established definitively which, if any, of these characteristics was actually closely linked with addiction.
So Dr. Parker and company observed some zebrafish from birth, rated them for various personality traits, then tried to get them hooked. And what they found was that in zebrafish, only one characteristic was strongly correlated with an addictive nature.
"Impulsivity," Dr. Parker concluded," is the closest thing we have to a causal factor for addiction."
In other words, science now has an important new weapon in the fight against addiction. There's no guarantee that the finding will be replicated in humans. And there's still plenty more work to be done before this research produces any useful results. But it does create the possibility of a future where we can spot the people most likely to develop harmful addictions, and perhaps make more of an effort to steer them away from dangerous substances. It's also a new important step in the direction of treatment tailored to the individual, which is the approach increasingly being favoured by the medical establishment. Finally, as Dr. Parker told me when I spoke to him afterwards, it may also help in identifying problems with relapse and withdrawal.
"It's unlikely that we'll ever be able to say we've 'beaten' addiction," he said. "It's such a complex set of behaviors—and we know that many addicts never do, and never will, find their way into the system. We hope that our research, and similar research to come, may put us in a better position to help people who want or need to engage with treatment services."