Oxytocin, the compound known as the love hormone and the cuddle chemical, deserves a new nickname, a new study suggests: the fear fighter.
When someone is suddenly frightened, two things happen: his heart rate increases and he tends to freeze momentarily. Until recently, it wasn’t known whether those two reactions occurred independently of each other or were governed by a single circuit in the brain.
The new study, involving rats, shows that when oxytocin levels are high, fear can raise the heart rate without provoking freezing behavior. Oxytocin is produced in the brains of both genders but particularly in women during lactation and childbirth; it promotes social bonding behavior, including the connection between mother and child.
"In a danger situation, you may want to maintain a fearful feeling but not be totally immobilized," said study researcher Ron Stoop, who researches psychiatric neuroscience at the University of Lausanne in Switzerland. For example, if a predator attacks, a mother may need to fight to protect her offspring, he said.
The study will be published tomorrow (July 1) in the journal Science.
Oxytocin and the brain
In the fear response, the signals that tell the heart to beat faster and the rest of the body to freeze originate in the amygdala, a part of the brain that is similar in humans and rats. Stoop and his colleagues determined that the amygdala cells that control heart rate respond differently to oxytocin than the amygdala cells that control the freezing response do.
The researchers also injected oxytocin directly into the brains of some rats. When the rats were then startled by a small electric shock, their heart rates always increased, but the rats that had received the extra oxytocin were far less likely to freeze.
"It’s like the animals still kind of feel the fear but have the possibility to respond," Stoop told MyHealthNewsDaily.
Why rat fear matters
Although there are vast differences between rodent and human biology, when it comes to fear, their brains have a lot in common with ours.
"There’s really nice correlations with the effects of the amygdala in terms of anxiety in rats and mice with humans," said Jeffrey Rosen, a professor of neurobiology at the University of Delaware.
Rosen, who was not involved with the study, called it very interesting. The finding may open the door for the development of "a possible medication for decreasing fear and anxiety without affecting heart rate," he said.
Moreover, the study sheds light on the biology of mothers' aggressive defense of their young. In response to a sudden threat, animals (including humans) with normal levels of oxytocin typically freeze, which may allow them to take in information about their surroundings while remaining less visible to any nearby predators.
However, "a mother that has a lot of offspring is typically releasing more oxytocin because it needs to lactate," Stoop said. As a result, "mothers are more aggressive" ? behavior better suited than freezing to protect one's brood.
Oxytocin levels also rise when an animal is thirsty, he said, which could cause a dehydrated animal to prioritize finding water over avoiding predators.
The study of fear is just the first step in better understanding the neurology of emotions, Stoop said. "An animal may be jealous, but it’s hard to study this precisely. Fear is better because it’s easier to observe."
Pass it on: If you're a mother fearlessly protecting her cubs, you may have oxytocin to thank for your behavior.