Mostly oxytocin's been associated with love. You make out with somebody, your body sends a huge shot of it to your brain and, all of a sudden, you want to move in together and start making babies (or at least doing the sorts of activities that result in babies). Or, once you go through labor and childbirth, your body's oxytocin-manufacturing mechanism goes into overdrive to make sure you'll love and cherish your baby instead of wanting to throw it out the window as revenge for all the agony it caused you.
Dr. Jelena Radulovic, a professor of psychiatry and pharmacology at Northwestern's Feinberg School of Medicine, believed this, too, when she set up an experiment on mice to test how the body reacted to different hormones during social interactions. She hypothesized that mice that produced more oxytocin would feel more positive effects from social interaction while those that produced more glutamate would have more negative feelings. It turned out that that oxytocin caused the mice to act more fearful.
That was 25 years ago. She's been studying oxytocin and fear ever since.
It turns out that after something socially stressful and horrible happens to you, oxytocin goes to work on your brain, enhancing your memory of the event. That's why you can still squirm over humiliations from elementary school. But the new thing Radulovic has discovered during a recent series of experiences is that oxytocin also increases your level of fear after a socially stressful episode.
"Social stress is the dominant stress now," she says. "We don't really have that much physical stress anymore."
This recent set of experiments was the first time Radulovic studied the production of oxytocin during a social situation. "We studied two different paradigms," she says, "memory and fear."
In the case of mice, that meant introducing them to a cage of strange mice that don't like interlopers. The mice had to spend ten minutes in the cage enduring attacks from the residents. To ensure maximum territorial behavior, all the mice in the experiment were male. ("We don't allow bleeding or open wounds," Radulovic says. "We screen the aggressors.") Six hours later, the mice were placed in a cage with one of their attackers and a previously unknown mouse. The mice with no oxytocin went right up to their attackers as though nothing had happened. The control mice tended to avoid the aggressors. But the mice with extra oxytocin really, really tried to get away from the aggressors. The oxytocin, it seemed, made the attacking mice that much more memorable.
In the second experiment, which was about fear, the mice again went through the crushing social defeat drill. But then, instead of reintroducing them to their attackers, Radulovic and her team put the mice in boxes that administered a small electrical shock. After 24 hours, they put the mice in the box again. There was no shock this time, but just as in the first experiment, the reactions ranged from nonchalance to freak-out based on the amount of oxytocin the mice produced. These seemed to indicate that the oxytocin triggered by social defeat led to fear of other things that happened at the same time but were unrelated.
"The social system works in a very distinct module of the brain," Radulovic explains. "It's very specific, independent of other types of stress or fear." This module is called the lateral septum, and it has a lot of oxytocin receptors. The module behaves the same in mice as it does in humans, which is why Radulovic believes her findings are relevant to the human population.
Oxytocin, she notes, is being used in anti-anxiety medicines, particularly those used to treat PTSD. She's concerned that, unless these drugs are used in a very specific social context, they can do more harm to the patients than good.
"Oxytocin should be one of the peptides that deserves more attention," she says.
In her next series of experiments, Radulovic hopes to test the effects of oxytocin on female mice because the time when the most oxytocin is produced is right after childbirth, but she has to figure out a way to engineer social defeat. Females don't fight like males do. She wonders if she can exploit the females' love of social stability by forcing them into new living arrangements with new cage-mates.
Someday she also hopes to study oxytocin during long-term social stress situations, like a kid who's being bullied at school or a worker with an unpleasant boss. "In more chronic situations," she says, "we want to see if the effect of oxytocin is more profound and if the body adapts."