New research challenges the role of ‘love hormone’ in relationships

New research challenges the role of ‘love hormone’ in relationships

Quirks and Quarks8:49The science behind the ‘love hormone’ may have a big problem

It’s official: There’s more to love than just one hormone. New research challenges the vital role of oxytocin, the so-called “love hormone,” in social bonding.

A recent study in the peer-reviewed journalNeuron has shown that prairie voles born without the ability to respond to oxytocin still formed strong bonds with their mates and young pups.

“Oxytocin may be an important player, but it’s not the only game in town,” study author Nirao Shah told Quirks & Quarks host Bob McDonald.

Much of the research around the function of oxytocin in pair bonding has involved prairie voles. They are among the very few mammals that, like humans, form long-term exclusive relationships, raise their young together, and even grieve the loss of their mates. And oxytocin has been thought of as the key ingredient to many of these behaviours in both voles and humans.

Researchers have previously studied what happened if the signal from oxytocin was disrupted in the voles’ brain by using drugs to block the oxytocin receptor — a kind of molecular door that lets the hormone in. The results were devastating: The rodents did not mate, and those who had litters left their pups to die of hunger.

A team of researchers at Stanford University decided to see what would happen if, instead of blocking the “door” for oxytocin, the voles were born with brains that didn’t have that door in the first place.

The researchers used the CRISPR gene editing technique to remove the oxytocin receptor in vole embryos.

“The advantage with genetics, especially the CRISPR technology being used, is that it’s sort of a molecular scissors that only makes the changes in the oxytocin receptor pathway and nowhere else,” said Shah, a professor of psychiatry, neurobiology, and obstetrics and gynecology at Stanford University.

They then observed how the voles behaved around each other and the rodents who had the oxytocin receptor system intact. In particular, the scientists looked for pair bonding behaviours. Those included huddling, where the voles cuddle up to their mates for a long time, along with voles showing an obvious preference for hanging out with their chosen mates over other rodents.

The results shocked the scientists.

“To our surprise, these animals that were completely lacking oxytocin receptor showed, for all intents and purposes, perfectly normal social attachment behaviours,” Shah said.

“No matter how many different ways we tried to test this, the voles demonstrated a very robust social attachment with their sexual partner, as strong as their normal counterparts,” study co-author University of California, San Francisco psychiatry researcher Devanand Manoli said in a press release.

Furthermore, voles without the oxytocin receptor turned out to be good parents, raising their small litters of pups to weaning.

Love finds a way

These study results offer a glimpse into how oxytocin shapes the brain mechanisms responsible for social behaviour, says Larry Young, a professor in the department of psychiatry at Emory University in Atlanta who was not part of the research team for this study. Young has extensively studied the role of oxytocin and vasopressin in social bonding and empathy in prairie voles as part of his work in the Silvio O. Conte Center for Oxytocin and Social Cognition at Emory University.

“It does suggest that oxytocin is shaping the brain circuitry in some way,” he told Quirks & Quarks in a phone interview. “So that if you’re born with it, it’s shaped in such a way that your circuitry depends on it. But if the animals don’t have any receptors from birth, there are some sort of adaptations in the circuitry or other genes to allow them to be able to perceive social interactions in the absence of oxytocin.”

As an analogy, Young explained, if you have an orchestra that’s led by a conductor, and suddenly the conductor is absent, the music may be out of sync. But if you have a street band that’s training without any conductor at all, they can still play great music.

“I think oxytocin is being the conductor,” Young said.

Prairie voles form monogamous, long-term pairs, where both rodents raise their young pups. These strong bonds are the reason why much of the science of social bonds comes from prairie vole studies. (Nastacia Goodwin)

Shah said other brain mechanisms may be at play when it comes to social bonding in the prairie voles born without the oxytocin receptors.

“There may be other hormone signaling pathways that work just fine, even in the absence of oxytocin. So if you take one out, the other pathway is still there and it can sort of give you normal social attachment behaviour,” he said.

Another possibility is that the voles developed another way to process oxytocin to compensate for the missing receptors — because, unlike rodents from past studies that had their existing oxytocin receptors blocked with drugs, the voles in this study lacked them from birth.

These findings help deepen our understanding of the role hormones like oxytocin play in behaviors of voles and humans alike. Past researchexplored using oxytocin in the treatment of social cognitive impairments, such as autism spectrum disorders or schizophrenia. But Shah says the present study calls for a more nuanced approach.

“Even though oxytocin may be important, just putting oxytocin back or providing more oxytocin doesn’t give you the ability to sort of bond magically,” said Shah.

“So our understanding needs to be more nuanced, there are other players or other signaling routes for oxytocin that we need to discover.”

Written and produced by Olsy Sorokina

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