Put in stressful situations, monkeys that rank lower socially are more likely to choose cocaine over food than are their high-status peers. This finding might be a key step in understanding the relationship among social status, stress and drug use.

In their research, Wake Forest University School of Medicine graduate student Robert Gould, with behavioral pharmacologist Michael Nader, PhD, and pharmacologist Linda Porrino, PhD, set up four social groups with four male macaques each. After the monkeys sorted into hierarchies, the researchers moved either a dominant or subordinate monkey to a cage located near a group of unfamiliar monkeys. They couldn't fight, but the lone monkey and the unfamiliar group could yell at each other, creating a stressful environment.

After 45 minutes, the researchers returned them to their normal enclosures where they could pull one of two levers: one that dispensed a banana-flavored food pellet or one that gave a dose of cocaine. Compared with their earlier recorded habits, the subordinate monkeys were far more likely than usual to choose cocaine. Conversely, the dominant monkeys were less likely to pull the cocaine lever after the stressful encounter.

Why the divergent behavior? Brain scans show that during the stressful situation, the subordinate monkeys exhibit decreased activation in brain areas associated with stress and anxiety management, whereas dominant monkeys show increased activation in the brain's pleasure-logging areas.

"Being able to aggress toward other animals was actually rewarding for them," Nader says, while the subordinate monkeys became stressed and anxious.

The finding may explain in part why stress makes some humans more likely to use drugs, says Gould. But, he cautions, there are many different stressors in human society. "It's a lot more than just social rank," he says.

--M. Price