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鈥攆ighting 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鈥�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.
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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).
鈥淲hat we found was surprising,鈥� 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鈥攖hat
neurotransmitters do not necessarily have the same effects on both sexes. 鈥淚t鈥檚
not a good idea at all to extrapolate from males to females,鈥� Gammie says.
鈥淚t is possible that nitric oxide plays a different role in maternal and male
aggression in humans,鈥� he adds. This would be likely, he says, if the same
effect turns up in a wide range of mammals.