The Homosexual Debate, 03/06/06
The Homosexual Debate, 03/06/06
Aug 7 2007, 01:21 PM
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Gender bender study breakthrough
Last Updated: 12:01pm BST 06/08/2007
Roger Highfield describes a mouse study that presents new twist on the quest to understand the difference between males and females
Scientists have found a way to turn female mice into aggressive, pelvic-thrusting masculine lotharios in an experiment that challenges established dogma.
For years, scientists have searched in vain for the bits of the brain that underpin the dramatic differences between males and females.
Now biologist say that all these efforts may have been in vain because such differences may not arise in the brain at all, thanks to a study that could may help provide profound new insights into the differences between the sexes.
The work comes up with the startling suggestion that both male and female brains contain the circuits for male and female behaviour but the ones that are actually used depend on signals from the body, which may turn one circuit on and the other one off.
The focus of sex specific behaviour in many species - though not humans - now shifts to a small sensory organ found in the noses of of most backboned creatures, except higher primates and birds.
The new work of the Harvard University and Howard Hughes Medical Institute team, published in the journal Nature, indicates that defects in this organ, known as the vomeronasal organ, lead female mice to act like males, solicting them, mounting them and thrusting them while abandoning nesting and nursing.
"These results are flabbergasting," says Prof Catherine Dulac. "Nobody had imagined that a simple mutation like this could induce females to behave so thoroughly like males."
It is as dramatic as showing a man could be made to behave like a woman at the flick of a switch, though the results do not apply directly to humans, which lack a vomeronasal organ.
Prof Dulac said the findings may open new avenues of investigation for research into the differences in the way men and women behave. Whether something as simple as this rules the complicated affairs of the human heart remains to be seen, though it looks unlikely.
"My work has nothing to do with humans," she told The Daily Telegraph. "The work may provide indirectly some new clues on how to understand and anayse differences between males an females in animals in general, but humans will be the hardest to study."
Working with Tali Kimchi and Jennings Xu, Prof Dulac studied female mice with a mutation that disables the vomeronasal organ, which works along with the nose to detect chemicals called pheromones that are used to attract mates.
They found that these females, when placed in a cage with a sexually experienced male, would engage in typically male courtship activity: chasing their cagemates, lifting the males' hindquarters with their snouts, and making complex ultrasonic squeaks that are part of the male mouse's mating ritual. Eventually, the female mutants would mount the hapless males, thrusting.
The male mice responded with increasing aggression toward the mutant females, eventually impregnating all of them. Once these females had given birth, Prof Dulac and her colleagues observed a striking lack of maternal behaviour: mutant females would readily wander away after about two days of motherhood, eventually abandoning the nest altogether.
While lactating mice will ordinarily attack male intruders and reject their attempts at courtship, the mutant females were docile toward males and appeared highly receptive to their overtures.
Another experiment to remove the vomeronasal organ showed that it represses male behaviour. "Our research suggests a new model where exactly the same neural circuitry exists in males and females," Prof Dulac says. For mice, at least, only the vomeronasal organ separates them in terms of behaviour.
What occurs in humans and other animals may be quite different, Prof Dulac noted, because the mouse depends largely on pheromones and its sense of smell, while humans and many other animals respond more to visual cues or a combination of signals from the senses.
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