Hormones, Not Just Love, Make Moms Tough

July 28, 2004 -- Nearly any mom can turn into a tiger if her kids are threatened. That's because a mother's love knows no bounds, right?

Well, that's not all of the story. It turns out that the fierce behavior that compels a mother to risk her own life in defense of her young may depend as much on chemistry and biology as on a mother's love.

Researchers at the University of Wisconsin-Madison have found evidence that a mother's protective behavior is regulated somewhat by the presence of a peptide hormone that is present in nearly all animals, including humans and mice.

Give mom a shot of corticotropin-releasing hormone (CRH), a peptide that acts on the brain to control behavior, and she will cower in the corner when a menacing male approaches her kids. Take it away and she'll kick his butt.

But that shouldn't take anything away from mom, says Stephen Gammie, assistant professor of zoology at the university.

"It doesn't make me feel any different" about something as romantic as a mother's love, Gammie says, "if I understand how it works."

Lactating and Fearless

Gammie and his colleagues, who published their research in the current issue of Behavioral Neuroscience, began tackling the biological basis of what is known as "maternal aggression" at a common starting point. Scientists have known for many years that fear and anxiety decrease in a mother during the period when she is lactating, or nursing her young.

The Wisconsin group wanted to know if that loss of fear accounted for the fierce behavior that most mothers can exhibit in the face of danger. Can it be that they will attack a threatening male primarily because they no longer fear him?

They suspected that CRH might be the substance regulating maternal aggression because other studies have shown that it "plays a big role in making you feel fearful and anxious," Gammie says.