Hormone Linked to Aggression in Mice

Research might yield insights into treatment for autism, experts say

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By Randy Dotinga
HealthDay Reporter

WEDNESDAY, Oct. 19, 2005 (HealthDay News) -- New research with mice offers more evidence that a specific hormone plays a major role in people's ability to take care of others and avoid conflict.

If the findings hold true for humans, scientists might get one step closer to a treatment for people with autism because they often lack an essential sense of empathy, researchers said.

The study, by a team of Japanese and American researchers, found that when mice were genetically engineered to not process the hormone oxytocin, the males became more aggressive and the females often forgot to take care of their babies.

Recent research has linked oxytocin -- no relation to the painkiller OxyContin -- to the ability of people to trust others. The new research is important because it expands on the role of oxytocin, said Paul Zak, director of the Center for Neuroeconomics Studies at Claremont Graduate University in Claremont, Calif.

"We're finding (oxytocin) is much more related to social behaviors, and social behavior deficits," said Zak, who worked on the research into oxytocin and trust.

In other words, oxytocin seems to be connected to how humans interact with each other -- and how the interactions can go wrong, he added.

Oxytocin is produced in the brain and released by the pituitary gland. Among other things, it seems to play a role in reproduction and perhaps even in the mysterious phenomenon called love.

Similar hormones appear in many animals, even including insects, said study co-author Katsuhiko Nishimori, a molecular biology researcher at Tohoku University in Sendai, Japan. In higher animals, the hormones seem to affect both reproduction and behavior.

Nishimori and colleagues bred mice that did not have "receptors" that would allow them to process oxytocin. Then they watched how the mice behaved.

The study findings appear in this week's issue of the Proceedings of the National Academy of Sciences.

The male mice were highly aggressive, quicker to attack intruders and more likely to fight them for a longer period. It wasn't clear, however, if the missing hormone might lower some other types of aggression.

The male mice were also more likely to forget the identity of females they had met.

As for the female mice, they sometimes forgot to retrieve their babies when they wandered off.

What does this all mean for people?

It's not entirely clear, Zak said, adding, "the extrapolation from mice to humans is a bit of a leap."

Still, it's possible the research could help scientists develop a treatment for people with autism. They can sometimes be aggressive or have trouble relating to other people, he said.

And, while researchers haven't proven it, some researchers suspect that problems with oxytocin may help explain autism, Zak said.

More information

To learn more about oxytocin, visit Colorado State University.

SOURCES: Katsuhiko Nishimori, Ph.D., molecular biology researcher, Tohoku University Graduate School of Agricultural Science, Sendai, Japan; Paul Zak, Ph.D., associate professor, economics, chairman, economics department, and director, Center for Neuroeconomics Studies, Claremont Graduate University, Claremont, Calif.; Oct. 17-21, 2005, Proceedings of the National Academy of Sciences

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