Commonly known as the “love hormone,” oxytocin plays a major role in social relationships — but more isn’t always better. A new mouse study published in the journal Biological Psychiatry shows that oxytocin amplifies the effects of social experiences — both good and bad. In fact, after negative social experiences, the presence of oxytocin in a particular part of the brain results in avoidance of unfamiliar social situations.
For the study, behavioral neuroscientists Natalia Duque-Wilckens and Brian Trainor worked with female California mice. When stressed, these mice often exhibit a form of social anxiety, shying away from unfamiliar mice instead of approaching them. However, the findings show that a single dose of a drug that blocks the activity of oxytocin restored normal social behavior in stressed females.
The findings are exciting because “for antidepressants like Prozac to have this same effect, it takes a month of daily treatment,” said Trainor, a professor in the University of California (UC), Davis Department of Psychology, College of Letters and Science.
The researchers expected the mice to behave in this manner based on their previous work showing that social stress increases the activity of oxytocin-producing cells in the brain and that females given intranasal oxytocin tend to avoid new social contexts.
Postdoctoral researcher Duque-Wilckens said that these findings support the theory that oxytocin amplifies the effects of social experiences. So rather than promoting only positive social interactions, oxytocin intensifies the experience of both positive and negative social interactions.
In a positive context, such as with family or friends, oxytocin could promote social approach behavior (hence its reputation as the “cuddling” hormone). However, in a negative context, like bullying, oxytocin could promote social avoidance.
But how can the same hormone have such different effects on behavior? The researchers found that two brain regions responded to oxytocin more strongly in females than males. These regions were the bed nucleus of the stria terminalis (BNST), a brain region known to control anxiety, and the nucleus accumbens, a brain region important for reward and motivation.
The team found that injecting an oxytocin blocker into the BNST, but not the nucleus accumbens, reversed the effects of stress on social behavior in females. Work by other researchers has suggested that oxytocin in the nucleus accumbens promotes rewarding aspects of social interactions.
These findings suggest that oxytocin can generate social anxiety or reward by acting in different areas of the brain. At times when oxytocin is acting in the BNST, drugs that block oxytocin could reduce social anxiety.
Trainor said a consistent theme in oxytocin research is that experience and the surrounding environment have important effects on how oxytocin affects behavior.
“Stressful social experiences appear to change which parts of the brain use oxytocin,” he said. “Understanding how this works in a mouse gives us new ideas on how we could use drugs targeting oxytocin to reduce social anxiety.”
Source: University of California, Davis