A new study from UC San Francisco and Stanford Medicine challenges a 30-year-old orthodoxy by suggesting that the oxytocin receptor may not serve the crucial function that scientists have attributed it to in the formation of social relationships.
Prairie voles reared without oxytocin receptors exhibited the same monogamous mating, bonding, and parental behaviors as wild voles, according to a research published online on January 27, 2023 in the journal Neuron. Moreover, unlike regular female voles, females without oxytocin receptors gave birth and produced milk, although in lower amounts.
Oxytocin is often referred to as the “love hormone,” but these findings suggest that oxytocin receptors aren’t solely responsible for the biology behind pair bonding and parenting.
Research into prairie voles helps elucidate the complexities of social bonding since they are one of the few mammalian species known to maintain lifelong monogamous partnerships.
Research conducted in the 1990s using medicines that block the binding of oxytocin to its receptor revealed that voles were unable to establish pair bonds, lending credence to the hypothesis that the hormone is crucial to social bonding.
This work was inspired by conversations between Manoli and Nirao Shah, MD, PhD, a neurobiologist formerly at UCSF who is currently on the faculty of Stanford Medicine. After learning about the oxytocin research as a teacher decades ago, Shah became fascinated in the biology of oxytocin and social attachment in prairie voles. As a postdoctoral fellow in 2007, Manoli joined Shah’s group to study the neurology of social bonding.
Based on the results of this research, oxytocin seems to be a very minor player in a much larger genetic scheme. This research took 15 years to complete, and it used cutting-edge genetic technology to determine whether or not the binding of oxytocin to its receptor is responsible for the formation of bonds between individuals. Prairie voles with non-functioning oxytocin receptors were created via CRISPR. They next examined whether or not the mutant voles were able to establish stable relationships with other voles. Mutant voles surprised scientists by pairing up as easily as their regular counterparts.
Birthing and Nursing
Manoli and Shah were surprised by the pair bonding, but they were even more surprised to learn that a high proportion of the female voles were successful at giving birth and nursing their young.
Manoli speculated that oxytocin had a more complex function in both delivery and nursing than was previously assumed. Despite the widespread belief that oxytocin is essential for labor, it was shown that female voles without receptors were fully capable of giving birth on schedule and in the same manner as normal animals.
There is now less confusion about the hormone’s function during labor thanks to these findings. Blocking oxytocin activity in moms experiencing preterm labor isn’t more effective than other methods for stopping contractions, despite its widespread usage in inducing labor.
However, when it came to lactation and feeding the puppies, the scientists were taken aback. It has been known for decades that oxytocin binding to its receptor is necessary for milk ejection and parental care. However, half of the mutant females were able to properly feed and wean their pups, suggesting that oxytocin signaling plays a role but is less crucial than previously thought.
Researchers Manoli and Shah were interested in the neurobiology and molecular underpinnings of pair bonding since this knowledge may lead to improved therapies for mental disorders like autism and schizophrenia that hinder individuals’ abilities to build or sustain social attachments.
Much expectation was placed on oxytocin clinical studies during the last decade as a potential treatment for these disorders. However, those findings were inconclusive, and they did not point to any obvious areas for improvement.
Scientists concluded that the present hypothesis, which holds that a single route or chemical is responsible for social attachment, is oversimplified, and their findings provide credence to this claim. From an evolutionary standpoint, they reasoned, this result is reasonable since attachment is crucial to the survival of many social creatures.