Mental Health photo
Viola Gad

Oxytocin, the feel-good bonding hormone released by physical contact with another person, orgasm and childbirth (potentially encouraging monogamy), might have a darker side. The love drug also plays an important role in intensifying negative emotional memories and increasing feelings of fear in future stressful situations, according to a new study.

Two experiments performed with mice found that the hormone activates a signaling molecule called extracellular-signal-related kinases (ERK), which has been associated with the way the brain forms memories of fear. According to Jelena Radulovic, senior author on the study and a professor at Northwestern University’s medical school, ERK stimulates fear pathways in the brain’s lateral septum, the region with the highest levels of oxytocin.

Mice without oxytocin receptors and mice with even more oxytocin receptors than usual were placed individually in a cage with aggressive mice to create a stressful social situation. The mice without receptors didn’t appear to remember the aggression, and didn’t show fear of the aggressive mice when reintroduced to the cage later. In contrast, the mice whose brains were full of oxytocin displayed intense fear when reintroduced to the aggressive mice.

In a subsequent experiment, the mice got to visit with the aggressive mice a few hours before being put in a box where they got a small, non-painful electric shock. A day later, upon going back to the shock box, the overly oxytocin’d mice exhibited much greater fear than the control group with normal oxytocin levels. The group with no oxytocin receptors didn’t show an enhanced fear of the box. This suggests that the hormone not only helps us remember negative social experiences, it intensifies anxiety in new stressful situations afterward.

Oxytocin has been studied as a way to combat anxiety and as a potential treatment for autism, though results have been mixed.

“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,” Radulovic said.

The study is online this week in Nature Neuroscience.