MONSTER MICE

By Anastasia Toufexis

SCIENTISTS AT JOHNS HOPKINS UNIversity in Baltimore knew something was wrong. Every morning when they checked the lab where their experimental animals were housed, they found one or two dead mice. At first they thought the rodents, whose genes had been manipulated to block production of a key neurotransmitter, might be having heart attacks. But when they looked more closely at the cages, they found bloodstains and tufts of fur, evidence suggesting an even more chilling possibility.

Was there a murderer among the mice? Indeed there was. In a paper published in Nature last week, a team from Johns Hopkins and Massachusetts General Hospital reported that by "knocking out" a gene essential to the synthesis of nitric oxide, an important neurotransmitter in the brains of mice and men, they had inadvertently created a strain of extraordinarily ferocious male rodents (females were unaffected).

Fast and fearless, these mice were six times as likely to pick a fight as normal, wild-type mice. And they scratched and bit so fiercely that researchers had to intervene to keep them from killing their rivals. Moreover, the males engaged in "excessive and inappropriate" sexual advances, mounting females despite "substantial vocal protestations." "It was very dramatic," says Dr. Solomon Snyder of Johns Hopkins. "The females would squeal, 'Rape! Rape! Rape!' but the males just wouldn't stop."

Researchers speculate that nitric oxide may effect the emotion-regulating areas of the brain, perhaps by putting the brakes on aggressive male behavior. Could a lack of nitric oxide help explain violent impulses in humans? Scientists caution against making facile comparisons. But they are watching the mad mice of Baltimore closely, looking for clues to treating similar behavior in humans.

--Reported by Alice Park/New York

With reporting by Alice Park/New York