Agression in mice linked to neurons active in sex: Moviestore collection LTD/Alamy; image via nature.com Cells that lie deep in the hypothalamus, known to be linked to violent behavior in male mice, were
shown, with the help of fluorescent tags, to be intertwined with cells
active during sex. Could a mix-up in these cells be responsible for
violent sexual behavior in some human males?
In the journal Nature, researchers Dayu Lin and David
Anderson, at the California Institute of Technology in Pasadena, report their experiments in which they try to observe what happens in a mouse brain when encountering male and female mice.
They used fluorescent tags to distinguish recently active neurons. They found that neurons within the ventromedial hypothalamus (VMH) was active during mouse fights, but they were also active during sex.
To further define what was happening, the researchers implanted male mice with electrodes capable of measuring the activities of single cells. Observing the mice in situations with other male mice, fighting, and with female mice, mating, they saw that different cells actually fired during fighting and sex. But there were some that cells that fired during both behaviors.
Their next experiment was to use optogenetics, a technique that allowed Lin and Anderson to fire the aggression neurons on command. Male mice responded by attacking intruding male mice and female mice, castrated male mice, anesthetized animals, and even an inflated laboratory glove. If sex had already begun, however, the males would not attack the females until post-coitus.
"I think there's every reason to think that this would be true in humans," said
Anderson. The hypothalamus is one of the brain's oldest structures, and the
region is also linked to aggression in monkeys."
They believe that their research is relevant to human males who commit violent sexual acts. "Maybe in those individuals there's some sort of miswiring in these circuits in
the brain, so the violent impulses and sexual impulses are not properly
segregated from each other."
Lin and Anderson were also able to tame aggression by altering a gene to silence aggression, although sexual interest remained.