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Oxytocin, also known as the "love molecule," is an appropriately many splendored thing. The naturally occurring brain chemical helps form sexual arousal, bonds between parents and children and even encourages generosity. On the other hand, oxytocin also reinforces social bonds at the expense of strangers - research indicates that oxytocin encourages ethnocentric favoritism.

A new study published in today's Nature Neuroscience states that oxytocin, so crucial to strengthening social bonds, can also strengthen traumatic memories and raise future fear and social anxiety. Confirming the suspicion of notebook-scribbling bedroom poets everywhere, loving and being hurt, in terms of brain chemistry, are closely related.

The researchers at Northwestern University found that oxytocin activates part of the brain to intensify the memory in stressful situations, a significant finding, as oxytocin is being tested as a possible anti-anxiety medication.

"Oxytocin is usually considered a stress-reducing agent based on decades of research," said Yomayra Guzman, a doctoral student at Northwestern and the study's lead author. "We showed how it enhances fear rather than reducing it and where the molecular changes are occurring in our central nervous system."

While oxytocin's domain of both fear and love might seem diametrically opposed, the feelings have complicated relationship in people. Think of the bond that emerges between war buddies, between horny teenagers at a scary movie, between the Old Testament God and the Israelites. Fight or flight and sexual arousal both engage the autonomic nervous system. Lead author on study, Jelena Radulovic, said that their research didn't specifically look at the relationship between fear and arousal, but she said this study combined evidence from other labs indicate it that it's possible that oxytocin is part of the link between the two.

The research team at Northwestern took three groups of mice - one group had normal oxytocin receptors, one group had an increased number and one group had none at all - and put them in cages with aggressive, bullying mice. Once they were thoroughly stressed out and socially defeated by the aggressive mice, they were removed from the cage for six hours.

When they were returned to the cage with the aggressive mice, the group with extra oxytocin receptors showed an "intense fear reaction," while the group without oxytocin receptors didn't appear to remember the aggressive mice and didn't show any fear.

Social stress is a leading cause of anxiety and depression, and since researchers see oxytocin as a potential anti-depressant, it's critical to understand how it functions in the brain under duress.

The researchers also noted that oxytocin presumably intensifies positive social memories, but as the research was on going, they declined to make any strong comment on it either way.

Scientists have high hopes for oxytocin - for everything from a diet aid to a pain reliever to an antidepressant; the love molecule may be all you need. But the hormone is still in the mouse-scaring phase of research, and its considerable power is proving quite complicated. Just as love continues to elude specific definition by the world's pop songwriters and poets, so too, the love molecule is proving to be a bit of a battlefield.