Aggression in male mice linked to 'girl power'.

Washington, October 2 (ANI): "Girl Power" may be key to male aggression, according to a new study.

Experts at the University of California, San Fransisco (UCSF) say that they have identified networks of nerve cells in the brain that are associated with how male mice defend their territory, and found that these cells are controlled by the female hormone oestrogen.

Writing about their findings in the journal Cell, the researchers said that their study suggested a pivotal role for oestrogen, as well as the enzyme aromatase that is responsible for oestrogen synthesis, in male territorial behaviour.

Dr. Nirao Shah, an assistant professor in the UCSF Department of Anatomy, said that ostrogen's role in the mating behaviours of those mice was less clear, which indicates that territorial and sexual behaviours are likely influenced by distinct and separate connections in the brain.

"This really changes the way we view male and female behaviours," said Shah, who also is affiliated with the UCSF programs in neuroscience and genetics and who last week received the 2009 Pioneer Award from the National Institutes of Health for his research.

"What we previously looked upon as a single unit of gender-related behaviour, we now see as a collection of separate behaviours controlled at least in part by distinct neural pathways," added the senior study author.

Shah pointed out that males and females across all sexually reproducing species display gender-specific behaviour in many areas, including mating, territorial marking, aggression and parental care.

Collections of cells form circuits in the brain, referred to as neural pathways, control these and other behaviours.

Shah said that both oestrogen and the male hormone testosterone are known to be essential in developing these circuits and in sex-specific behaviour.

However, added the researcher, it has been unclear as to what is the precise role of these hormones, and how they may interact genetically to control these behaviours.

He insisted that his team's work filled in at least one piece of the puzzle by suggesting that the conversion of testosterone in the brain to oestrogen by the enzyme aromatase is critical to developing and activating brain circuits that control male territorial behaviour.

Calling the potential conclusions of the study intriguing, Shah said: "We show that exposure to oestrogen neonatally can alter adult sex-specific behaviours in mice."

However, those findings did not appear to apply to sexual behaviour.

While male mice reliably mate frequently with females, the oestrogen-treated females showed no difference from untreated females when exposed to normal females that were sexually receptive, or in heat.

But the estrogen-treated females did not display typical female sexual behaviour: they mated much less frequently with males and even attacked and chased them.

The researchers proposed that these aromatase-expressing regions of the brain could form an interconnected network that regulates sex-specific behaviours.

Shah, however, insisted that more studies on the role of the development of sex-specific neural pathways were required, and hat many additional factors, including genetics and socialization, could contribute to sexual differentiation. (ANI)

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