Oxytocin, a hormone that plays a role in intimacy and social bonding, is being investigated as a treatment for anxiety, depression, and PTSD. But a new study with mice raises important questions about the differing effects the hormone has on men and women.
Says Brian Trainor, an associate professor of psychology at the University of California, Davis:
“Most clinical studies investigating oxytocin as a treatment for depression or anxiety include only males,” “It’s important to include both men and women in these studies.”
Trainor and colleagues 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 had no effect. When non-stressed females received oxytocin, social motivation was reduced. This effect of oxytocin is similar to the effect of social stress.
“Reduced social motivation can be part of a depression-like syndrome,” says Trainor.
Too Much Oxytocin?
They 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.
Michael Steinman, a UC Davis neuroscientist involved in the study, used a molecular marker to show that these oxytocin-producing cells were also more active in females that experienced stress.
“This may help explain why oxytocin nasal spray makes females avoid social contact even though they did not experience social stress,” says Steinman.
Clinical studies have found that women with depression or PTSD have elevated oxytocin levels. Usually this result has been thought to reflect an increased drive for social support. The results of Trainor and 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 says. “If correct, inhibiting oxytocin action might have unanticipated benefits.”
The surrounding environment also influenced the effects of oxytocin. If mice were tested in a familiar home cage instead of a new environment, oxytocin reduced stress-related behaviors in males and females.
This finding shows that the effects of oxytocin depend whether the environment is familiar or unfamiliar.
“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 says.
Michael Q. Steinman, et al. Sex-Specific Effects of Stress on Oxytocin Neurons Correspond With Responses to Intranasal Oxytocin Biological Psychiatry DOI: http://dx.doi.org/10.1016/j.biopsych.2015.10.007