It's a sex thing

2019-03-07 02:02:01

By Alison Motluk A BRAIN chemical that dampens aggression in males has the opposite effect on females. The finding highlights the importance of recognising that research done on one sex may not be relevant to the other, say scientists in Baltimore. A few years ago, Stephen Gammie and his colleagues at Johns Hopkins University discovered that when they took male mice and snipped out a gene that produces the neurotransmitter nitric oxide, the mice became very aggressive—fighting with other males and forcing themselves on females. The researchers wanted to confirm that the same thing happened in female mice deprived of that gene. Female mice tend to be aggressive only when they are guarding newborn pups. So the Hopkins team examined the behaviour of 22 new mothers—13 normal mice and 9 that had been genetically engineered to lack nitric oxide. Then they watched what happened when a strange male approached them, something that usually triggers an attack by protective mothers. The researchers predicted that the engineered females, like males, would show more aggression. But they found the opposite. While normal mothers viciously attacked intruders, those without nitric oxide hardly bothered to intervene at all (Journal of Neuroscience, vol 19, p 8027). “What we found was surprising,” says Gammie. He concludes that, unlike the males, females actually need nitric oxide to show aggression. The finding highlights a little-known fact, say the researchers—that neurotransmitters do not necessarily have the same effects on both sexes. “It’s not a good idea at all to extrapolate from males to females,” Gammie says. “It is possible that nitric oxide plays a different role in maternal and male aggression in humans,” he adds. This would be likely, he says,