A recent study from the University of California, Berkeley, suggests that oxytocin, often called the “love hormone,” is also important for forming friendships. Oxytocin is known to be released in the brain during activities such as sex, childbirth, breastfeeding, and social interactions. It has been linked to feelings of attachment and trust but also has associations with aggression.
Research on prairie voles—rodents known for forming stable relationships similar to humans—has raised questions about oxytocin’s role in long-term mate bonding and parenting. Previous studies showed that while oxytocin is not essential for these bonds or behaviors, its absence leads to delays in their formation.
The UC Berkeley team, led by Annaliese Beery, associate professor of integrative biology and neuroscience, focused on how oxytocin affects peer relationships rather than just mating bonds. “Prairie voles are special because they allow us to get at the neurobiology of friendship and how it’s similar to and different from other types of relationships,” said Beery.
Beery and graduate student Alexis Black found that prairie voles lacking oxytocin receptors took longer than normal voles to form close peer relationships. These animals typically display behaviors such as huddling together or grooming each other when bonded. “Oxytocin seems to be particularly important in the early formation phase of relationships and especially in the selectivity of those relationships: ‘I prefer you to this stranger,’ for example,” Beery said. “The animals that didn’t have intact oxytocin signaling took longer to form relationships. And then when we challenged those relationships by making new groups, they lost track of their original partners right away.”
The genetically modified voles used in this research were developed at UC San Francisco by Dr. Devanand Manoli’s lab. These voles did not show typical social rewards from selective attachments; they were less motivated to seek out friends and less avoidant or aggressive toward strangers.
“In other words, oxytocin is playing a crucial role not so much in how social they are, but more in who they are social with, their selectivity,” Beery explained.
Further analysis using a novel nanosensor technology developed at UC Berkeley revealed changes in how oxytocin was regulated and released in the brains of receptor-deficient voles. “That helped us understand the feedback consequences of lacking this receptor, and how oxytocin signaling was altered in the brain,” said Beery.
The study was published August 8 in Current Biology.
Beery’s research extends beyond laboratory work with prairie voles; she has conducted field studies comparing social behavior across various rodent species both within South America and North America. Her findings suggest that selective peer partnerships may be widespread among rodents—even more common than monogamous pairings—and could have evolutionary significance.
“While most rodents prefer to interact with unfamiliar individuals, it turns out that the majority of vole species we’ve tested in our early trials form peer-partner preferences, which is what we call these selective friendships. So there seems to be this widespread tendency to bond,” Beery noted. She added: “But only a couple of those species are also monogamous… I think this familiarity preference is deeply rooted.”
Previous work co-authored by Beery indicated that even without functioning oxytocin receptors, prairie voles can still develop monogamous bonds and parent normally—though relationship formation takes longer without the hormone’s signaling pathway.
In experiments testing friendship bonds specifically, normal prairie voles formed preferences for peers within 24 hours while those lacking receptors needed up to a week. When placed among groups where they could choose whom to spend time with—similar to mingling at a party—receptor-deficient animals did not show a preference for familiar companions as wild-type animals did.
“Wild-type animals form this incredibly robust preference within one day of co-housing, but the null mutants have no sign of a relationship after 24 hours,” said Beery.” After a week…the lifetime partners look no different from each other.” She concluded: “Our conclusion from that experiment is that oxytocin isn’t required to have a relationship, but it’s really important in those early phases…to facilitate it happening quickly and efficiently.”
Additional tests showed normal female prairie voles worked harder (by pressing levers) for access to mates or friends compared with strangers—a pattern not seen among receptor-deficient animals except regarding mating partners.
Lack of oxytocin signaling delayed relationship formation and weakened long-term peer connections; however, affected animals were also less aggressive toward unfamiliar individuals.“You can see contributions of oxytocin signaling to both sides of selectivity,” Beery observed.“On the prosocial side…it’s involved in wanting to be with a known friend or peer; while on the antisocial side…it’s aiding in rejecting an unfamiliar animal.”
To investigate changes caused by missing receptors further, researchers used carbon nanotube-based nanosensors created by Markita Landry’s group at UC Berkeley.These sensors allowed them to monitor real-time release patterns of oxytocin molecules directly inside vole brains.Landry reported,“Komatsu and I found no excess of oxytocin in the voles’ brains.In fact ,oxytocin was being released in lower amounts from fewer sites…”This observation points toward reduced availability rather than compensatory increases elsewhere .
Other contributors included Jiaxuan Zhao , Scarlet Taskey , Nicole Serrano (UC Berkeley), Ruchira Sharma (UCSF), Natsumi Komatsu (now University Of Illinois). The project received support from National Science Foundation CAREER award 2239635 as well as NIH grant R01MH132908 .
