Oxytocin, also known as "the love hormone," has long been known to play a number of roles in orgasms, bonding, and maternal behaviors. But according to a new study, the hormone may be equally linked to feelings of emotional pain, including anxiety and fear.

"Oxytocin is usually considered a stress-reducing agent based on decades of research," Yomayra Guzman, a doctoral student and lead author of the study, said in a press release. "With this novel animal model, we showed how it enhances fear rather than reducing it and where the molecular changes are occurring in our central nervous system."

They discovered that most fear responses pass through the lateral septum — a part of the brain — which has a large number of oxytocin receptors. They believed that by inducing a fear response, they would be able to see how the oxytocin receptors responded.

They induced this fear response using a molecule that is activated by oxytocin. The molecule, known as extracellular signal regulated kinases (ERK), triggers negative social memories and the future anxiety that's associated with them. After a negative social memory, ERK becomes active for six hours.

For the first experiment, the researchers used three groups of mice; one group was missing its oxytocin receptors, another had a normal amount, and the third had an increased amount of receptors. Each group was placed into a cage, separately, with a group of aggressive mice. All the mice in the three groups experienced social defeat.

Six hours later, the mice were put back into the cages with the aggressive mice — all three groups reacted in different ways. The mice that didn't have oxytocin receptors, which meant that the hormone couldn't access their brains, didn't appear to remember the aggressive mice, and therefore, showed no fear. However, the mice that had an increased amount of receptors, which meant that their brains were overwhelmed by the hormone, showed an even more intense fear of the aggressive mice than the control mice, which had normal amounts of the receptors.

In the second experiment, the same three groups of mice were exposed to brief, startling electric shocks, six hours after the first experiment. Twenty-four hours later, the mice were put into the same box where they experienced the shock, to see how they would respond. Those without receptors showed no fear of the box, while the group with extra receptors showed a more intense fear, and the group with a normal amount showed an average fear.

Chronic social anxiety, or social phobia, occurs when people's everyday interactions cause them to feel anxious, fear, self-consciousness, embarrassment, and it can lead to depression. On the contrary, positive social interactions enhance well-being. These findings are important, the researchers say, because oxytocin is currently being tested as an anti-anxiety drug.

"By understanding the oxytocin system's dual role in triggering or reducing anxiety, depending on the social context, we can optimize oxytocin treatments that improve well-being instead of triggering negative reactions," Jelena Radulovic, co-author of the study and the Dunbar Professor of Bipolar Disease at Northwestern University Feinberg School of Medicine, said in the release.


Guzman Y, Tronson N, Radulovic J, et al. Fear-enhancing effects of septal oxytocin receptors. Nature Neuroscience. 2013.