Aggressive behavior in animals may result in posturing, teeth baring or challenges related to protecting territory, offspring or food. In humans, it can lead to violence and death, and the causes are not always readily apparent. But where does it originate?
One path to the origins of aggression is in the brain, where neurobiologists study the role of hormones on behavior. That is the broad focus of research being undertaken by Heather Caldwell, associate professor of biological sciences at Kent State University, in a project funded by a new $400,000 National Science Foundation grant.
Caldwell will look for evidence in early brain development of how a particular hormone can affect aggressive behavior in adulthood. Caldwell has long been interested in how brain hormones affect behavior, specifically, two closely linked hormones, oxytocin and vasopressin. While researchers, including Caldwell, have looked at the role vasopressin plays in aggression, oxytocin is more often associated with cooperative behavior.
But evidence is building, she said, that oxytocin also plays a role in aggression. Her research team will look at when and where in the brain, during early development, it is involved in organizing the brain circuits that are important to adult male aggressive behavior.
Her hypothesis is that exposure to oxytocin in utero is important for the development of normal aggressive behavior in adulthood. If the developing brain is not exposed to oxytocin, the result may be altered aggressive behavior in adulthood.
She studies this in male laboratory mice, since males typically display more aggressive behavior then females. While human behavior is “vastly more complicated” than mice, she expects to learn more about the origins of aggression.
“If we understand the basics, it may provide insights into other species, including humans,” she said.
Her study will identify “the timing window in which oxytocin signaling helps to organize the neural circuits that underlie male aggressive behavior.”
The brain hormones do not themselves cause behavior, but they modulate it. The key is how they interact with a receptor, in this case, a protein in the cell’s membrane. The fetal mouse does not make oxytocin early in development, but it has oxytocin receptors ready to signal. As Caldwell describes it, “the catcher’s mitt is there.”
Oxytocin comes from the mother — it is the hormone that spurs uterine contractions and milk ejection. While the blood-brain barrier can limit what transfers from the mother’s blood to the fetal brain, there is evidence that oxytocin crosses that barrier and gets in.
Caldwell’s research team will map the receptors for oxytocin in the developing brain to see where the oxytocin from the mother could interact. They will study the mice through development into adulthood, monitoring their behavior and looking for a relationship between the early developmental exposure to oxytocin and later aggression.
The study will be the first to look at the prenatal and possibly fundamental role for oxytocin in the development of adult aggressive behavior.
Caldwell developed an interest in the effect of hormones on behavior after working with loggerhead sea turtles in North Carolina, where she earned her undergraduate biology degree.
Her interest in how hormones affected their behavior led her to pursue a doctorate at Georgia State University, which has a large NSF-supported Center for Behavioral Neuroscience. She spent four years as a postdoctoral fellow at the National Institutes of Health and joined the Kent State faculty in 2007.