“The mutant females were aggressive toward strange males, sniffed at their genitals and mounted them,” Dulac says. The mice re-mained functionally female, however, and in fact mated and gave birth. Then came the second surprise: the mutant mothers quickly abandoned their nests and young and went off to ex-plore their cages—much as males would. The experiment, Dulac adds, implies that the neuronal circuits for “male”behavior exist in the brains of female mice and that the animals’ VNO, by sensing pheromones, con-trols which sexualbehavior reper-toire is expressed.
Although humans and other higher primates lack a func-tional VNO, the researchers think that different sensory controls (such as visual or auditory cues) may be in-volved in activating sexual behavior in these species. [For more about phero-mones in humans, see “Sex and the Secret Nerve,” by R. Douglas Fields; SCIENTIFICAMERICANMIND, February/March 2007.]The next step, Dulac says, will be to analyze male mice without a functioning VNO to see if they display femalelike behaviors