Are you able to bond with out the ‘love hormone’? These cuddly rodents present it is potential

There’s more to love than a single hormone.

That’s according to a study of prairie voles that have been genetically engineered to ignore signals from the “love hormone” oxytocin.

The study, published in the journal Neuron, comes after decades of research suggesting behaviors like pair bonding and parenthood depend on oxytocin. Many of these studies have involved prairie voles, which mate for life and are often used to study human behavior.

“Oxytocin may be ‘love potion number nine,’ but one through eight are still in play,” says Dr. Devanand Manoli, author of the study and psychiatrist at the University of California, San Francisco.

The finding is important but not surprising, says Sue Carter, a psychology professor at the University of Virginia and distinguished university researcher at Indiana University, Bloomington, who was not involved in the study.

“The process of forming a secure social bond over a very long period of time is too important to be limited to a single molecule,” says Carter, who helped credit the link between oxytocin and social behavior in prairie voles more than 30 years ago discover.

Carter believes that oxytocin is the central player in behaviors such as pair bonding, parenting, and lactation. But she says animals born without the ability to respond to the hormone appear to find other ways to replicate behaviors critical to their survival.

A big surprise

The discovery that pair bonding occurs without oxytocin surprised the team that conducted the experiment.

“We were shocked because it was really, really not what we expected,” says Manoli, who worked with a team that includes Dr. Nirao Shah from Stanford University and Dr. UCSF’s Kristen Berendzen.

The team’s experiment was designed to disrupt pair bonding and other oxytocin-related behaviors in prairie voles. These include parenthood, milk production, social bond formation, and socially monogamous pair bonding.

/ Nastacia Goodwin

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Nastasia Goodwin

A new study shows that prairie voles don’t need oxytocin receptors to form pair bonds.

“One of the most adorable behaviors is this cuddling behavior,” says Manoli. “Sometimes they preen themselves. Sometimes they just fall asleep because it’s very soothing. And that’s very specific to the pair-bonded partner.”

Previous studies had found that these behaviors disappear when scientists use drugs to block oxytocin in adult prairie voles. So the team expected they would achieve a similar result by using a gene-editing technique to eliminate the oxytocin receptor, a molecule that allows cells to respond to the hormone.

This time, the team took fertilized eggs from female prairie voles, altered the genes, and then transferred the embryos to females that were hormonally ready for pregnancy.

The result was puppies that appeared normal. And as these pups grew up, like other prairie voles, they formed pair bonds.

The females could even produce milk for their offspring, albeit in smaller quantities than unaltered animals.

“My first response was, okay, we have to do this three more times because we have to make sure it’s 100% real,” says Manoli. But repeated experiments confirmed the finding.

More than a “love hormone”?

It’s still a mystery what drives pair bonding in the absence of oxytocin. But it’s clear, says Manoli, that “due to evolution, the parts of the brain and the circuitry responsible for forming pair bonds don’t rely on it [only] on oxytocin.”

In retrospect, the result is understandable, since pair bonding is essential for the survival of a prairie mouse. And evolution tends to favor redundant systems for critical behaviors.

The finding may help explain why giving oxytocin to children with autism spectrum disorder doesn’t necessarily improve their social functioning, Manoli says.

“There is no one way,” he says. “But these complex behaviors have really complicated genetics and complicated neural mechanisms.”

One possible explanation for the result is that if prairie voles lack an oxytocin system almost from conception, they are able to resort to other systems to develop normally, Carter says.

That could mean using a different molecule, Carter says, vasopressin, which also plays a role in social bonding in both humans and prairie voles. And there may be other molecules yet to be discovered.

A full understanding of the biology underlying social bonds is critical to understanding human behavior, says Carter. It could also explain why people generally don’t thrive without positive relationships, especially during childhood.

“We can live without fine clothing. We can live without too much physical protection. But we can’t live without love,” says Carter.

That could be why we might be able to love without oxytocin.

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