Oxytocin is often called the 'bonding hormone' because it is involved in many social, sexual and maternal behaviors in mammals. Scientists have long documented the presence and effects of oxytocin during specific physiological conditions and behavioral responses, but little is known about the specific mechanisms by which this neuropeptide functions. Recently, however, researchers at New York University (NY) teased apart some of the physiology by which oxytocin promotes maternal behaviors in mice (Nature 520, 499–504; 2015).

As with humans, parenthood for mice involves a learning curve, and virgin mice often do not exhibit the maternal behaviors that experienced mothers demonstrate. For example, experienced mothers often notice the distressed call of an isolated pup and will promptly retrieve the pup, whereas virgin mice generally fail to notice or retrieve isolated pups.

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Researchers Robert Froemke and colleagues were able to elicit this behavior in virgin mice by housing them with experienced mothers and litters. This behavior was more common and arose sooner among virgins with artificially increased oxytocin levels compared with controls. “It was remarkable to watch how adding oxytocin shifted animal behavior, as mice that didn't know how to perform a social task could suddenly do it perfectly,” said Bianca Marlin, the first author of the paper, in a press release.

The researchers also identified a key location where this behavioral response takes place. By pharmacologically inactivating only the left auditory cortex, they impaired the retrieval behavior in experienced maternal mice and, using antibody labels, they confirmed that the left auditory cortex contains more oxytocin receptors than the right.

This is not to say that oxytocin simply causes maternal retrieval behavior, however. When the researchers used antagonists to block oxytocin receptors in the left auditory cortex, experienced mothers continued exhibiting the retrieval behavior. It seemed, therefore, that oxytocin chiefly encourages females to notice the stimulus and learn the behavioral response, but it is not needed to summon that response each time.

“Oxytocin turns up the volume of social information processed in the brain,” said Froemke, and his team confirmed this by monitoring individual neurons in the auditory cortex during oxytocin administration. These findings reveal how oxytocin participates in 'bonding' behaviors and demonstrate a general mechanism by which neuromodulators can promote attention and learning. Froemke considers this a strong example for future studies and intends to continue exploring the role of oxytocin in the brain.