Social motivation in voles differs by species

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image: Prairie voles are naturally social rodents that provide an opportunity to study the biology of social bond formation.
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Credit: Berry Lab

A study published today in eLife.

The results indicate what happens in the mouse brain when different types of relationships form and show that social motivations may vary by individual, gender and species. Since hormones and similar brain structures are involved in social interactions in many species, including humans, this new information may lay the foundation for a better understanding of some of the foundations of social differences.

Voles make good model animals for studying social behaviors because they are social creatures by nature. Some mouse species, such as the prairie voles, form lasting social bonds with both mates and same-sex mates. On the other hand, prairie stallions only form societies to help them survive the winter and then detach in the warmer months.

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“We wanted to determine why mice of these two species spend time in social contact,” says first author Annaliese Berery, who directed this research in her lab at Smith College in Northampton, Massachusetts, US, and is currently in the Department of Integrative Biology at the University of California, Berkeley, United State. “Specifically, we wanted to find out what role social drive plays in their behavior, or to what extent social selectivity relates to avoiding strangers.”

To answer these questions, Perry and her colleagues trained both prairie voles and prairie voles to push a rod to receive food as a reward. Then they traded food rewards with a short reach for a familiar muzzle of the same species, or a stranger, to see how many times the mouse would push the rod to approach the other animal. With each successive press of the bar, it became more and more difficult to reach the other mouse, as the animals needed to press the bar again for more access.

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“There were surprising differences in species and sex in the people that the mouse would work to be closer to,” Berry says. Her team found that female prairie mice worked harder to see familiar mice more than strangers, but male prairie mice did not show this preference for their acquaintance. Instead, the males worked hard to reach any female, but showed less interest in males. But the males still huddled with familiar animals when they were together. Prairie voles, which were only females, did not work as hard as female prairie voles to reach familiar animals.

Together, the results suggest that prairie voles find social interactions with familiar animals rewarding, whereas prairie voles were more likely to tolerate friends and family on unfamiliar animals but these interactions were not significantly motivated.

Finally, the researchers discovered that individual difference in behavior is linked to the density of receptors in the brain for oxytocin – a hormone associated with social interaction. Animals with more oxytocin receptors in a part of the brain called the nucleus accumbens worked harder to socialize. By contrast, animals with more oxytocin receptors in a part of the brain called the bed nucleus than the terminal stria were more likely to be aggressive toward other animals.

“Our study demonstrates the difference between social reward and social selectivity,” says co-author Sarah Lopez, who worked on the study as a research student in the Berry Social Endocrinology Laboratory at Smith College and is now a medical student at the University of Pittsburgh, US. “We’ve shown that selectivity can come from avoidance and lack of avoidance, as well as from social reward.”

Berry adds: “Knowing more about how the mechanisms that underpin social relationships across species and sexes are similar and different will help us understand which mechanisms are universal and which are species-specific. This insight may, in turn, aid our understanding of how species-typical social behavior patterns evolve over time.”

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Emily Packer, Director of Media Relations

eLife

e.packer@elifesciences.org

+44 (0) 1223 855373

About eLife

eLife is a non-profit organization created by funders and led by researchers. Our mission is to accelerate discovery by operating a platform for research communications that encourages and recognizes the most responsible behaviours. We aim to publish work of the highest standards and relevance in all areas of biology and medicine, including Neurology, while exploring new creative ways to improve how research is evaluated and disseminated. eLife receives financial support and strategic guidance from Howard Hughes Medical Institute, The The Knut and Alice Wallenberg Foundation, The Max Planck Society And wellcome. Learn more through https://elifesciences.org/about.

To read the latest neuroscience research published in eLife, visit https://elifesciences.org/subjects/neuroscience.


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