You know that stomach-flipping excitement we feel for someone we are falling in love with? You may also be familiar with the gut-wrenching anxiety that can creep in. Well, the hormone that makes us feel love and social bonding can also cause emotional pain, researchers at Northwestern University have found.

The hormone oxytocin enhances social memory in a part of the brain called the lateral septum, an area the researchers say plays a role in emotional responses. Though that means oxytocin strengthens positive social memories, it also reinforces stressful social situations, which can stay with us for a long time and spark feelings of anxiety or fear down the road.

So if a social encounter is negative, oxytocin activates the lateral septum and intensifies that memory. In addition, this intensification has a self-perpetuating effect, whereby the hormone can make us fearful during future stressful incidents.

Oxytocin has been researched by scientists looking for an anti-anxiety drug, so the present researchers expected that the hormone would access positive emotions in the memory. In a surprise twist, they found that it actually enhances negative emotions under stressful situations.

Experiments with oxytocin in mice

The researchers set up two experiments with mice. The first one involved three groups of mice:

  • Group 1: The mice were missing their oxytocin receptors
  • Group 2: The mice had an increased number of oxytocin receptors
  • Group 3: Control group in which the mice had a normal number of receptors.

These three groups were placed individually in cages containing aggressive mice so that the subject mice would experience a socially frustrating situation. Then 6 hours later, the mice were returned to the cages with the aggressive mice.

The mice without receptors did not seem to remember the aggressive mice or exhibit fear, whereas the group with the increased receptors exhibited a great deal of fear and tried to avoid the other mice.

A later experiment replicated the first one, except rather than putting the mice back in the aggressive cages 6 hours later, the researchers gave them a mild, non-painful electric shock. Then 24 hours later, the mice were placed back in the same box, only this time they did not receive a shock. The mice with an increased number of oxytocin receptors exhibited a great amount of fear, whereas the mice without receptors did not show much fear at all.

The two experiments show that oxytocin strengthens the memory of negative social events, and it also elevates fear and anxiety in the future.

Impact for humans

The researchers note that the findings from these experiments are noteworthy because chronic stress leads to anxiety and depression, whereas positive social experiences can lead to emotional health.

Jelena Radulovic, senior author of the study, says:

"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 wellbeing instead of triggering negative reactions."

Through these experiments, Jelena Radulovic and her team discovered that a signaling molecule known as ERK becomes activated for 6 hours after a negative social interaction, and that oxytocin in turn strengthens the negative memory of that social interaction. Since oxytocin is being considered for an anti-anxiety compound, these findings are particularly relevant.

"Oxytocin is usually considered a stress-reducing agent based on decades of research," says study author Yomayra Guzman. "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."