Neuroscience: The hard science of oxytocin

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As researchers work out how oxytocin affects the brain, the hormone is shedding its reputation as a simple cuddle chemical. In April 2011, Robert Froemke and his team were reprogramming the brains of virgin mice with a single hormone injection.

Before the treatment, the female mice were largely indifferent to the cries of a distressed baby, and were even known to trample over them. But after an injection of oxytocin, the mice started to respond more like mothers, picking up the mewling pup in their mouths. Froemke, a neuroscientist at New York University’s Langone Medical Center in New York City, was monitoring the animals’ brains to find out why that happened.

At first, the mice showed an irregular smattering of neural impulses when they heard the baby’s cries. Then, as the oxytocin kicked in, the signal evolved into a more orderly pattern typical of a maternal brain. The study showed in unusual detail how the hormone changed the behaviour of neurons. “Oxytocin is helping to transform the brain, to make it respond to those pup calls,” Froemke says.

Oxytocin has been of keen interest to neuroscientists since the 1970s, when studies started to show that it could drive maternal behaviour and social attachment in various species. Its involvement in a range of social behaviours, including monogamy in voles, mother–infant bonding in sheep, and even trust between humans, has earned it a reputation as the ‘hug hormone’. “People just concluded it was a bonding molecule, a cuddling hormone, and that’s the pervasive view in the popular press,” says Larry Young, a neuroscientist at Emory University in Atlanta, Georgia, who has been studying the molecule since the 1990s.

“What we need to start thinking about is the more fundamental role that oxytocin has in the brain.” That view has led some clinicians to try oxytocin as a treatment for psychiatric conditions such as autism spectrum disorder. But the early trials have had mixed results, and scientists are now seeking a deeper understanding of oxytocin and how it works in the brain. Researchers such as Froemke are showing that the hormone boosts neuronal signals in a way that could accentuate socially relevant input such as distress calls or possibly facial expressions. And clinical researchers are starting a wave of more ambitious trials to test whether oxytocin can help some types of autism.

The work is leading to a more sophisticated view of the hormone and its complex effects on behaviour — one that will take many types of expertise to refine. “The oxytocin field has just matured and ripened enough to draw in researchers from traditionally separate fields, catapulting this forward,” says Young.

Oxytocin’s story starts back in the early 1900s, when biochemists discovered that a substance from the posterior pituitary gland could promote labour contractions and lactation. When scientists later discovered the hormone responsible, they named it oxytocin after the Greek phrase meaning ‘rapid birth’. Oxytocin is produced mainly by the brain’s hypothalamus; in the 1970s, studies revealed that oxytocin-producing neurons send signals throughout the brain, suggesting that the hormone had a role in regulating behaviour.  Nature  Original webpage at Nature

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