Turning certain neurons on or off in fly brains creates wildly erotic or sexually withdrawn animals, a new study shows. The findings point to new players in a complex circuit activated in the fly brain during courtship.
Fruit fly males go to great lengths to cozy up to females, singing and even jumping to attract their lover's attention. Researchers had long known that a handful of sex-specific neurons must be present in male brains for the first steps of this courtship ritual to commence. But it still wasn't clear whether other parts of the central nervous system help regulate the flies' elaborate wooing techniques.
With this in mind, Sue Broughton, now at University College London, and her colleagues at New York University and the Neurosciences Institute in La Jolla, California, selectively switched neurons on and off in adult male flies. To do this, they used specially bred flies with genes that could be turned off in groups of nerve cells at high temperature. To see how courting is affected when neurons are hyperactivated, they used flies with a version of a gene that was stuck in the "on" state in clumps of nerve cells. Then they observed whether the animals could still properly court females. Upping the activity of neurons in one region of the brain, they found, made flies court like crazy, while stifling nerve cell activity in the same brain zone left males disinterested.
Most of these nerve cells cluster near a region in the fly brain called the lateral protocerebrum, the team reports in the 6 April issue of Current Biology. Previously, scientists had found that this region was responsible for the sex-specific phase of the wooing rituals. The work "begins to get at the mechanisms as to how a particular behavior is carried out by the brain," says author Ralph Greenspan, a neurogeneticist at the Neurosciences Institute.
The authors have made "a very classy advance in brain behavioral studies," says Jeffrey Hall, a neurogeneticist at Brandeis University in Waltham, Massachusetts. The study helps sort out how sex-specific components of the central nervous system interface with other parts of it, he adds.