In a new study, University of California scientists have discovered that oxytocin, also called the "love hormone" due to its role in intimacy and social bonding, might have different effects in men and women. Most interesting, in some situations it may actually trigger anxiety. The results come at the same time as clinical trials on oxytocin's ability to treat anxiety, depression and post-traumatic stress disorder (PTSD) are underway.

In the experiments, the researchers administered doses of oxytocin to male and female mice using a nasal spray. In males, they found that it increased their motivation for social interaction in stressful situations, which is consistent with previous research. However, in stressed females, they found that it had no effect, and in non-stressed females it reduced social motivation, which can be likened to social stress

"Reduced social motivation can be part of a depression-like syndrome," Brian Trainor, co-author of the study, said in a press release.

Why does oxytocin affect males and females differently? Trainor and his team examined this question and found that stress affects the production of oxytocin - nerve cells in the brain create more oxytocin in females than males following a stressful event, and these cells are also more active in females enduring stress.

"This may help explain why oxytocin nasal spray makes females avoid social contact even though they did not experience social stress," said Michael Steinman, who also co-authored the study.

The researchers also found that oxytocin's effects are environmentally dependent - oxytocin had an inhibitory effect on stress-related behaviors in mice who were tested in their home cage as opposed to a new environment.

The findings can be used to further understand the effects of oxytocin in males and females and how this translates into the ways that they cope with mental disorders. Studies have shown that women with depression or PTSD have increased oxytocin levels, and many believe that this is why they tend to seek help more often than men.

"Our results show that stressed females have both reduced social motivation and increased oxytocin. It's possible that oxytocin might contribute to a depression-like syndrome in females," said Trainor. "If correct, inhibiting oxytocin action might have unanticipated benefits."