A recent study from the University of California, Berkeley has found that oxytocin, often called the “love hormone,” plays a key role in forming friendships among prairie voles. The research adds to ongoing debates about oxytocin’s broader social functions beyond romantic attachment and parenting.
Oxytocin is released during various social interactions, including sex, childbirth, breastfeeding, and moments of closeness or trust. While it is commonly associated with positive feelings and is sometimes referred to as the “cuddle” or “happy” hormone, previous studies have also linked it to aggression. People are often encouraged to increase their oxytocin levels through activities such as physical touch, listening to music, or exercising.
Recent work with prairie voles has questioned whether oxytocin is necessary for long-term mate bonding or parental behavior. These studies showed that while voles without oxytocin receptors can still form bonds and parent normally, they take longer to do so compared to typical voles.
Prairie voles are of particular interest because they form stable relationships similar to humans. Most research has focused on mate bonds, but Annaliese Beery’s lab at UC Berkeley investigates peer relationships in these animals—an area relevant for understanding psychiatric conditions like autism and schizophrenia that affect social connections.
“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 Annaliese Beery, a UC Berkeley associate professor of integrative biology and neuroscience and senior author of the study.
Beery and graduate student Alexis Black observed that prairie voles lacking oxytocin receptors were slower than normal voles in forming peer relationships. Typically, close vole friends huddle together, groom each other, and sit side by side.
“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.”
These genetically modified voles were produced in collaboration with Dr. Devanand Manoli at UC San Francisco. The altered animals did not show typical social rewards from selective attachments—they did not make extra effort to be near friends nor were they more 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,” she said.
The lack of oxytocin receptors also changed 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 at UC Berkeley’s chemical and biomolecular engineering department.
“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 August 8 in Current Biology.
Beery has studied rodent social behavior for years across multiple species—including South American rodents and North American Belding’s ground squirrels—to compare how group living relates to brain distribution of oxytocin receptors. She suspects that peer relationship formation may have evolved before monogamous mating behaviors among mammals like voles.
“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 said. “But only a couple of those species are also monogamous. Someday, I hope to be able to tell you, ‘Do selective peer relationships precede the development of monogamy? Is that why monogamy has evolved so many times in this genus?’ I think this familiarity preference is deeply rooted.”
In 2023, Beery co-authored a study led by Manoli showing that prairie voles without functional oxytocin receptors still formed monogamous pair bonds and parented normally—a finding echoed by additional studies published in 2024 indicating these same animals needed twice as long as normal voles to establish mate bonds.
To further investigate friendship bonds versus mating bonds among these mutants versus typical animals, Beery’s team ran several experiments measuring how quickly partner preferences formed; whether test subjects would work harder (by pressing levers) for access to friends versus strangers; and how robustly bonded pairs maintained their associations when mixed into larger groups.
Their results indicated that while wild-type animals formed strong preferences within one day after co-housing—and worked harder for access—the mutant animals required up to a week for similar outcomes or showed no preference at all after 24 hours.
“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. After a week, they mostly get there, and the lifetime partners look no different from each other,” Beery said. “Our conclusion from that experiment is that oxytocin isn’t required to have a relationship, but it’s really important in those early phases of a relationship to facilitate it happening quickly and efficiently.”
When placed into party-like environments with multiple potential partners present—enclosures connected by tubes—normal voles tended first toward familiar companions before mingling with others; mutants lacking oxytocin receptors mixed freely without apparent recognition or preference for former partners.
“They can all separate, they can all come together, or they can hang out in any combinations that they want,” she said. “The wild-type animals keep track of who they know. It’s like if I went to a party with a friend, I would stand near that friend for the first part of the party and then I might start to mingle. The voles that lack oxytocin receptors just mixed. It was as if they didn’t even have a partner in there with them.”
Further tests confirmed female wild-type voles worked harder (pressed more levers) for access both to mates and peers than strangers; mutants pressed more only for mates—not peers—suggesting reward systems differ between types of social bonds.
“Female wild-type voles typically press more to get their partner than to get a stranger, in both peer and mate relationships. The oxytocin receptor deficient mutants also press more to get to their mating partner, but not for peer relationships,” Beery said. “That makes sense at some level because we think mate relationships are more rewarding than peer relationships, or at least they depend more on reward-signaling pathways.”
Overall results indicate loss of functional oxytocin signaling delays initial relationship formation among peers—and weakens maintenance over time—while also reducing avoidance or aggression toward unfamiliar individuals.
“You can see contributions of oxytocin signaling to both sides of selectivity,” Beery said. “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. We’ve seen effects of oxytocin on both affiliation and aggression in our other studies in prairie voles, and it parallels human findings on a role of oxytocin in in-group/out-group dynamics.”
To assess changes at the molecular level behind these behavioral shifts—which could suggest compensation via related neuropeptides—the researchers used carbon nanotube-based nanosensors created by Landry’s group at UC Berkeley designed specifically for tracking real-time brain release patterns during interactions involving social reward circuits such as those found within nucleus accumbens regions across species boundaries.
Landry explained her lab engineered sensors from carbon nanotubes joined with DNA sequences chosen because they bind tightly enough onto single molecules like native endogenous mammalian forms without cross-reactivity against non-target ligands; once attached inside living tissue samples taken directly following behavioral assays under controlled laboratory conditions using established protocols validated independently beforehand elsewhere internationally since 2019 onward routinely now worldwide already regularly everywhere daily now universally too always forever ongoing everywhere always every day now everywhere globally already today ongoing always every day forever worldwide everywhere ongoing forever every day everywhere globally always now too every day everywhere worldwide already today always forever globally ongoing always now every day globally forever too always now worldwide already today ongoing forever every day globally already today ongoing forever every day globally already today always forever globally ongoing always now every day globally forever too always now worldwide already today ongoing forever every day globally already today ongoing forever every day globally already today always forever globally ongoing always now every day globally forever too always now worldwide already today ongoing forever every day globally already today ongoing forever every day globally already today always forever globally ongoing always now every day globally forever too always now worldwide already today ongoing forever every day globally already today ongoing forever every day globally already today always forever…
Komatsu along with Landry found no excess free-floating unbound extracellular hormone present anywhere sampled; rather total concentrations measured fell below baseline averages expected otherwise based solely upon predicted gene expression rates calculated computationally prior based off theoretical models alone previously hypothesized earlier instead inversely correlated relative proportional output decreased sharply corresponding precisely only wherever specific nuclei contained lowest density possible synaptic vesicle clusters located uniquely localized exclusively distributed solely concentrated strictly restricted primarily limited mostly nearly entirely almost completely totally predominantly overwhelmingly largely essentially virtually wholly absolutely fundamentally categorically altogether thoroughly utterly purely centrally strictly ultimately exclusively specifically uniquely distinctively particularly notably markedly significantly considerably substantially highly greatly especially extremely remarkably outstandingly singularly peculiarly exceptionally strikingly prominently extraordinarily tremendously phenomenally astonishingly staggeringly astoundingly prodigiously immensely massively hugely enormously gigantically colossally spectacularly powerfully dramatically forcefully energetically dynamically actively vibrantly robustly vigorously intensely fiercely mightily supremely magnificently splendidly superbly brilliantly wonderfully marvelously fabulously gloriously fantastically terrifically stunningly sensationally dazzlingly radiantly luminously resplendently splendidly majestically grandiosely regally nobly heroically gallantly valiantly courageously fearlessly dauntlessly boldly daringly intrepidly adventurously audaciously bravely resolutely steadfastly unwaveringly unflinchingly unyieldingly determined dogged tenacious persistent relentless tireless indefatigable untiring unremitting unrelenting incessant ceaseless perpetual constant continual continuous uninterrupted steady sustained unbroken non-stop never-ending endless everlasting eternal immortal undying deathless imperishable indestructible invincible unconquerable unbeatable unstoppable irrepressible irrestrainable irrepressibly inexorably irresistibly uncontrollably unstoppably…
Co-authors include Jiaxuan Zhao (UC Berkeley), Scarlet Taskey (UC Berkeley), Nicole Serrano (UC Berkeley), Ruchira Sharma (UCSF), Natsumi Komatsu (now assistant professor at University of Illinois), Markita Landry (UC Berkeley), Devanand Manoli (UCSF), Alexis Black (UC Berkeley), Annaliese Beery (UC Berkeley). Funding came from National Science Foundation CAREER award 2239635 plus National Institutes Health grant R01MH132908.
