Instead of gaining increased aggressiveness like the males, the females lost their aggressive behavior in the one context where it normally showed up, when they were nursing pups and a strange male mouse came around, putting the pups in danger of an attack. For the new study, scientists switched over to voles, which are also rodents and look like a stout mouse or rat, but are more closely re-lated to lemmings and muskrats than to mice. Also, while voles are relatively nonaggressive, previous research had shown that males experience a dramatic increase in aggression toward intruders after mating. For the new study, Gammie and co-author Randy Nelson, a professor of psychology and neuroscience in the Krieger School, exposed mated and nonmated male voles and female voles with pups to intruders, and then examined the levels of citrulline in their brains. The increase was focused on an area of the brain known as the paraventricular nucleus.
Researchers plan to see if they can suppress nitric oxide production in the voles with a drug.
If so, they'll test to see if using this drug in mated male voles reduces their aggression levels. Scientists may also test the possibility of links between nitric oxide and the monogamous behavior of the voles. Gammie and Nelson's research was funded by grants from the National Institutes of Health and the National Institute of Mental Health. It was presented at the recent annual meeting of the Society for Neuroscience in Miami Beach.