A new study found that men and women react differently toward oxytocin, a potential treatment for anxiety, depression and post-traumatic stress disorder.

Known as the “love hormone” for its role in intimacy and social bonding, it may even trigger anxiety in some circumstances, according to researchers at the University of California Davis.

In a series of experiments at the UC Davis Department of Psychology, the team administered doses of oxytocin with a nasal spray to male and female mice. Some of the mice were bullied by an aggressive mouse, an experience that reduces motivation to associate with unfamiliar mice. Consistent with previous studies, oxytocin increased the motivation for social interaction in stressed males.

However, in stressed females, oxytocin was not found to trigger any effect. When non-stressed females received oxytocin, social motivation was reduced, an effect that is similar to that of social stress. Reduced social motivation can be part of a depression-like syndrome, said one of the study’s co-authors, Brian Trainor, an associate professor of psychology.

Trainor and his colleagues found important differences in how stress affected the production of oxytocin. After stress, nerve cells in the brain produced more oxytocin in females but not in males.

Behavioural neuroscientist Michael Steinman used a molecular marker to show that these oxytocin-producing cells were also more active in female mice that experienced stress. “This may help explain why oxytocin nasal spray makes females avoid social contact even though they did not experience social stress,” he said.

Clinical studies have found that women with depression or PTSD have elevated oxytocin levels. This result has commonly been thought to reflect an increased drive for social support. The study results of Trainor and his colleagues suggest an alternate possibility.

“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,” Trainor said. “If correct, inhibiting oxytocin action might have unanticipated benefits.”

The surrounding environment also influenced the effects of oxytocin. When mice were tested in a familiar home cage instead of a new environment, oxytocin reduced stress-related behaviours in males and females. This finding shows that the effects of oxytocin depend on whether the environment is familiar or unfamiliar.

Trainor said the lab’s findings have implications for studies investigating the utility of oxytocin as a therapeutic.

Most clinical studies investigating oxytocin as a treatment for depression or anxiety include only males, he noted. “It’s important to include both men and women in these studies. The effect of oxytocin may be different if administered by an unfamiliar person or by a person with whom the patient has a personal relationship,” Trainor concluded.

Depression is the leading cause of disability worldwide, according to Beyondblue. In Australia, it is estimated that 45 percent of people will experience a mental health condition in their lifetime. Around one million Australian adults are reported to have depression in any one year, while over two million have anxiety.

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