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Elite Macaques Get No Kick From Cocaine
22 January 2002 (All day)
According to Henry Kissinger, power may be the ultimate aphrodisiac; now researchers think it may also be superior to drugs. Scientists say an experiment with macaques indicates that socially dominant animals are less prone to getting hooked on cocaine.
Past research on macaques found that socially dominant animals enjoy a boost in their dopamine D2 receptors, part of the brain's reward circuitry involved in addiction. And in 1999, an intriguing study on humans found that individuals with low levels of D2 receptors especially liked receiving injections of speed in the form of methylphenidate, whereas those with the highest levels disliked the drug. But no experiment had linked social dominance with susceptibility to drug abuse.
To determine whether a link exists, neuropharmacologist Michael Nader of Wake Forest University School of Medicine in Winston-Salem, North Carolina, and his colleagues first scanned the brains of monkeys housed individually to measure their base number of D2 receptors. Then they put the animals into five groups of four, where they naturally formed social hierarchies. When the researchers measured the D2 receptors 3 months later, they recorded a 20% increase in receptor binding capacity--indicating more action in reward centers--in the highest-status monkeys.
The researchers then introduced drugs into the equation. After teaching the monkeys to press levers to obtain banana pellets, they hooked them up to intravenous tubes and observed their lever-pressing activity for either a jolt of saline solution or a hit of cocaine. While the most subordinate monkeys clearly preferred cocaine to saline, the dominant monkeys' lever-pressing for cocaine "was not significantly different" from their lever-pressing for saline, says Nader, whose study appears in February's issue of Nature Neuroscience. To Nader, that means the elevated level of D2 receptors may protect the macaques against drug abuse, though precisely how is uncertain.
Neuropharmacologist Michael Kuhar of Emory University in Atlanta calls the study "a very interesting finding." He adds, "it shows the impact of environment and perhaps personality and circumstance on vulnerability and on the desire to take drugs." Kuhar points out, though, that the dominant monkeys get their kicks from aggressive behaviors, such as attacking subordinate animals, so it might take them longer to get interested in cocaine. The study needs to be replicated, he says, in order for its results to become widely accepted.