Men influenced by oestrogen too

Gender-specific behaviour patterns are often chalked up to testosterone in men and oestrogen in women, but a new study explains why the hormone issue isn't so clear cut.

The male hormone testosterone doesn't work in ways that had been assumed when it comes to masculinising the brain during development and making males behave a certain way when they're adults, researchers found.

"It was known that testosterone and oestrogen are essential for typical male behaviours in many vertebrate species," said study senior author Dr. Nirao M. Shah, of the anatomy department at the University of California, San Francisco. "However, how these two hormones interact to control masculinisation of the brain and behavioir remained to be established."

How the study was done

Shah and colleagues genetically engineered mice to get rid of a pathway thought to play a role in how animals become masculinised. Yet, they found that the mutant mice still acted like males -- fighting and marking territory -- but with some differences. In particular, the extent and frequency of typical male behaviours varied between the mutant mice and the other mice.

The study, published in the April 29 issue of the journal Neuron, found that estrogen, which is virtually undetectable in the circulation of most male species, can be derived from circulating testosterone in males. In the brain, this testosterone-derived estrogen can control many behaviors that are typically linked to males.

"Our findings in conjunction with previous work suggest a model for the control of male pattern behaviours in which oestrogen masculinises the neural circuits for mating, fighting and territory marking, and testosterone and oestrogen signaling generate the male typical levels of these behaviours," Shah said. "It will be interesting in future studies to identify the molecular and circuit level mechanisms that are controlled by these hormones." - (HealthDay News, April 2010)