COCAINE ADDICTION LINKED TO SOCIAL ORDER IN MONKEYS

Dominant Ones Less Likely To Get Hooked

Monkeys higher up on the social ladder are less likely to become addicted
to cocaine, a finding that could explain why some people are more prone to
addiction, researchers at Wake Forest University said.

In a study that will be published in next month's Nature Neuroscience, the
scientists put 20 macaque monkeys in small groups. After they had created a
social ranking, the scientists allowed the monkeys to inject themselves
with cocaine.

The monkeys that were dominant in the groups - those with better access to
food and more able to control the other monkeys - were less likely to
become addicted.

"The positive spin on that is environment enrichment - changes in the
environment that enhance someone's condition - can protect them from drug
abuse," said Michael A. Nader, an associate professor for the departments
of physiology and pharmacology and of radiology, who conducted the study
along with nine colleagues.

"The negative is that stressors - in this case a social stressor - can also
impact the likelihood that a drug will have a greater potential for abuse,"
he said.

It wasn't just the stress of being on the bottom of the social scale that
made the monkeys use more cocaine. Using Positron Emission Tomography, a
type of scanning, the researchers found that the monkeys' brains changed
once their social patterns were established.

After three months in the social groups, the dominant monkeys grew more
areas in their brains where dopamine - a natural chemical in the brain that
triggers the feeling of being high - could be absorbed.

Cocaine blocks the dopamine receptors, allowing the dopamine - and its good
feeling - to stay around longer.

Dominant monkeys ended up with 20 percent more dopamine receptors in their
brains than the subordinate monkeys.

That allowed them to absorb the dopamine at nearly the rate they would
without the cocaine, so they never used enough to become addicted.

"There is a typical characteristic to how they respond. We can say that the
drug is serving as a reinforcer. In the dominant monkeys, it was not. They
did not press the lever very much to get the cocaine," Nader said.

The subordinate monkeys had fewer receptors, so the cocaine was able to
block them more effectively. The dopamine stayed in their brains longer,
and they grew to like the cocaine.

The monkeys will stay on the cocaine and will be used in other experiments,
Nader said.

Despite being addicted to cocaine, the monkeys are all in good health, he said.

"We limit the amount of cocaine that they can get. So that there's a very,
very small likelihood that the cocaine will have any kind of adverse affect
on them," Nader said. "You could not walk back there and tell which monkey
had cocaine and which didn't."