Prairie voles can form close bonds without oxytocin

Oxytocin – the so-called “love hormone” – has been considered for decades to be essential for the development of social attachments in a variety of animal species. However, according to a new genetic study led by the University of California, San Francisco (UCSF) and Stanford University, prairie voles can still form enduring attachments with their mates and provide parental care even without oxytocin receptor signaling. 

Prairie voles are one of the few monogamous mammalian species, forming life-long partnerships called “pair-bonds.” Pair-bonded voles share parental responsibilities, and prefer the company of their partners over other members of the opposite sex, actively rejecting potential new partners. Previous research which used drugs to block oxytocin from binding to its receptor found that voles lacking oxytocin binding were unable to pair-bond.

However, by using a groundbreaking genetic manipulation technique called CRISPR to generate prairie voles lacking oxytocin receptor signaling, the researchers found that these genetically-altered voles could still form pair-bonds just as easily as normal voles.

“We were all shocked that 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,” said study lead author Devanand Manoli, a neuroscientist at UCSF.

Following this surprising discovery, the experts investigated whether oxytocin receptor signaling is similarly dispensable for other functions, such as parturition, parenting, and milk release during lactation. “We found that mutant voles are not only able to give birth, but actually nurse,” reported co-author Nirao Shah, a neuroscientist at Stanford. In fact, both male and female mutants engaged in usual parental behavior, such as huddling, licking, or grooming, and were capable of rearing their offspring to weaning age.

However, the mutant voles had limited milk release compared to the normal ones, which caused fewer of their pups to survive to weaning age. In addition, the pups that managed to survive were smaller compared those of normal voles. The fact that voles could nurse at all is highly different from what has been observed in studies involving oxytocin-deficient mice. According to the researchers, this could be due to the inbred nature of lab mice strains in contrast to the genetically heterogenous voles. 

“It could be that inbreeding in mice has selected for a large dependence on oxytocin signaling, or this may represent a species-specific role of oxytocin receptor signaling,” Shah explained.

“For at least the last ten years people have been hoping for the possibility of oxytocin as a powerful therapeutic for helping people with social cognitive impairments due to conditions ranging from autism to schizophrenia. This research shows that there likely isn’t a magic bullet for something as complex and nuanced as social behavior,” Manoli concluded.

The study is published in the journal Neuron.

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By Andrei Ionescu, Earth.com Staff Writer

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