WASHINGTON (Reuters) - Female mice became sexually voracious and tried to mate like males after scientists disabled a small sensory organ, casting fresh light on how gender-specific behavior develops in animals.
The difference seems to lie in how male and female mice use the vomeronasal organ to process pheromones, said Catherine Dulac, the Harvard biologist who led the research published in the journal Nature Sunday.
Pheromones are chemical signals that many animals, including humans, use to communicate socially and sexually.
The vomeronasal organ, found in the noses of some animals but not in people or higher primates, is a key processing center for pheromones.
Scientists had long attributed aggressive male mating tactics to a testosterone-induced hard-wiring of male brains.
“Here you have females that never had male hormones but have perfectly male behavior,” Dulac said in a telephone interview.
In female mice, pheromones normally suppress male sex behaviors and activate female ones, the research suggests.
“This comes as a surprise to think that the neural circuitry for male behavior had been sitting in the female brain all this time,” said Mark Breedlove, a neuroscientist at Michigan State University not involved in the study.
The researchers said they bred female mice without a gene critical to the vomeronasal organ’s function. They also sliced the organ from otherwise normal adult females.
In both cases, the females pursued cage mates aggressively, sniffing their rears and mounting them. They turned to other male mating behaviors, such as pelvic thrusts, while eschewing typically female roles like nesting and nursing.
“You feel sorry for the males. You imagine they’re confused,” Breedlove said in a telephone interview.
The females did not limit themselves to males, with some trying to mate with other females. It turns out female mice need the vomeronasal organ to tell the sexes apart, just as males have in earlier studies, the researchers said.
The role of pheromones in humans is more controversial.
“We’re not so olfactory or pheromonal as mice or rats,” Breedlove said.
“On the other hand, it does make you wonder if humans also contain both sets of neural circuitry in the brain, and if something other than odors is responsible for determining which set we’ll use as we grow up.”