A recent study from the University of California, Berkeley, has found that oxytocin, often called the “love hormone,” is also important for forming friendships. The research focused on prairie voles, a rodent species known for their stable social relationships similar to those in humans.
Oxytocin is commonly associated with attachment and trust during activities such as sex, childbirth, breastfeeding, and other social interactions. While it has also been linked to aggression, it is frequently referred to as the “cuddle” or “happy” hormone. People are often encouraged to increase their oxytocin levels through physical touch, music, and exercise.
However, recent research using prairie voles has questioned whether oxytocin is essential for long-term mate bonding or parenting behaviors. These studies have shown that while oxytocin is not strictly necessary for these bonds to form, its absence causes delays in establishing them.
The Beery lab at UC Berkeley directed its attention toward peer relationships among prairie voles rather than mate bonds. According to Annaliese Beery, associate professor of integrative biology and neuroscience at UC Berkeley and senior author of the study: “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.”
Beery and Alexis Black, an integrative biology graduate student and co-first author of the study, observed that prairie voles lacking oxytocin receptors took longer than normal voles to form peer relationships. In typical behavior, close vole friends huddle together and groom each other.
“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 study were developed at UC San Francisco by Dr. Devanand Manoli’s laboratory. These animals lacked social rewards usually derived from selective attachments; they did not put effort into being with friends nor showed much avoidance or aggression 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 said.
The absence of oxytocin receptors also affected how oxytocin was regulated and released in the brain. This was measured using a new nanosensor developed by postdoctoral fellow Natsumi Komatsu and Markita Landry, a professor at UC Berkeley’s Department of Chemical and Biomolecular Engineering.
“That helped us understand the feedback consequences of lacking this receptor, and how oxytocin signaling was altered in the brain,” said Beery.
The findings were published on August 8 in Current Biology.
Beery has studied social bonds among rodents for years—especially peer or friendship relations—and has conducted fieldwork comparing behavior across different rodent species as well as Belding’s ground squirrels from North America. She believes understanding these behaviors across species can help clarify which traits are unique versus generalizable among mammals.
She noted that while most rodents prefer unfamiliar individuals’ company over familiar ones, many vole species tested show preferences for specific peers—a tendency she describes as selective friendships—even though only a few vole species are monogamous.
“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… So there seems to be this widespread tendency to bond,” Beery said. “But only a couple of those species are also monogamous…”
Beery previously contributed to a 2023 study led by Manoli which found that prairie voles without functioning oxytocin receptors still formed mating bonds and parented offspring like normal voles—though later work revealed these receptor-deficient animals needed about twice as long as normal ones to establish such bonds.
In further experiments focusing on friendship rather than mating bonds: normal voles took about 24 hours to develop partner preference; receptor-deficient voles required up to a week before showing any preference between familiar peers versus strangers. When placed between two others with access controlled by lever presses (a measure used by researchers), mutant voles showed no clear preference after one day but caught up after about a week.
“Our conclusion from that experiment is that oxytocin isn’t required to have a relationship,” Beery explained,”but it’s really important in those early phases…to facilitate it happening quickly and efficiently.”
Additional tests involved placing pair-bonded voles into mixed groups where normal animals tended initially toward familiar partners before mingling; mutants showed no such preference even when original partners were present.
In another test measuring willingness (via lever pressing) for access either to mates or peers: wild-type females worked harder for both mates’ or friends’ company compared with strangers; mutants pressed more only for mates—not friends—suggesting mate relationships may depend more heavily on reward pathways tied closely with oxytocin signaling.
Lack of proper signaling delayed relationship formation overall while weakening long-term peer connections—but also reduced avoidance or aggression toward strangers among mutant animals.
“You can see contributions of oxytocin signaling to both sides of selectivity,” Beery said.“On the prosocial side…wanting…a known friend…on the antisocial side,…rejecting an unfamiliar animal….It parallels human findings on…in-group/out-group dynamics.”
To examine if missing receptors changed how much oxytocin was released (potentially compensated by related neuropeptides), researchers used carbon nanotube-based nanosensors created by Landry’s group—which fluoresce upon binding with oxytocin molecules—to track hormone activity inside key brain regions like the nucleus accumbens involved in social reward processing across species.
Komatsu and Landry found no excess release; instead there was less available oxytocin released from fewer sites within these areas.
Other contributors included Jiaxuan Zhao, Scarlet Taskey and Nicole Serrano (UC Berkeley), Ruchira Sharma (UCSF), along with support from agencies such as the National Science Foundation (CAREER award 2239635) and National Institutes of Health (R01MH132908). Komatsu now serves as assistant professor at University of Illinois.
