Prairie voles don’t need ‘love hormone’ oxytocin to bond, study finds: Shots

There is more to love than a single hormone.

That’s the conclusion of a study of prairie voles genetically altered to ignore signals from the “love hormone” oxytocin.

The study, published in the journal neuron, comes after decades of research suggesting that behaviors such as pair-bonding and parenting depend on oxytocin. Many of those 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 is still in play,” says Dr. Devanand Manoli, an author of the article and a psychiatrist at the University of California, San Francisco.

The finding is important but not surprising, said Sue Carter, a professor of psychology at the University of Virginia and leading university scientist 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 confined to a single molecule,” says Carter, who helped discover the link between oxytocin and social behavior in humans more than 30 years ago. prairie voles.

Carter believes oxytocin is the central player in behaviors including pair bonding, parenting and breastfeeding. But she says animals born without the ability to respond to the hormone seem to find other ways to mimic behaviors critical to their survival.

A big surprise

The finding that pair bonding occurs without oxytocin came as a surprise to the team conducting the experiment.

“We were shocked because that really wasn’t what we expected,” says Manoli, who worked with a team that included Dr. Nirao Shah of Stanford University and Dr. Kristen Berendzen of UCSF.

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

“One of the behaviors that’s really the cutest is this crouching behavior,” says Manoli. “They sometimes nurse. Sometimes they just fall asleep because it’s very soothing. And that’s very specific to the couple-bonded partner.”

Previous studies had shown that this behavior disappears when scientists use drugs to block oxytocin in adult prairie voles. So the team expected to get a similar result using a gene-editing technique to eliminate the oxytocin receptor, a molecule that allows cells to respond to the hormone.

This time, the team removed fertilized eggs from female prairie voles, edited the genes, and then placed the embryos in females that were hormonally ready for pregnancy.

The result was puppies that looked normal. And when these pups grew up, they paired up just like other prairie voles.

The females were even able to produce milk for their offspring, although the amount was less than in unaltered animals.

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

More than one “love hormone”?

It is still a mystery what causes pair bonding in the absence of oxytocin. But it is clear, says Manoli, that “because of evolution, the parts of the brain and the circuits responsible for pair bond formation do not depend on [only] on oxytocin.”

In hindsight, he says, the result makes sense because pair bonding is essential to a prairie vole’s survival. And evolution tends towards redundant systems for critical behavior.

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

“There is no single path,” he says. “But rather, this complex behavior has really complicated genetics and complicated neural mechanisms.”

One possible explanation for the result is that when prairie voles lack an oxytocin system almost from conception, they may use other systems to develop normally, Carter says.

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

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

“We can live without pretty clothes. 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.