Love Will Carry On: the oxytocin system and social behavior

‘Cause your love’s got the best of me

And, baby, you’re making a fool of me

You got me sprung and I don’t care who sees

~ Crazy in Love by Beyoncé ~

And your memory

And how every song reminds me

Of what used to be

That’s the reason I’m so sick of love songs

So tired of tears

So done with wishing

She was still here

~ So Sick by Ne-Yo ~

I know that you are something special

To you, I’d be always faithful

I want to be what you always needed

Then I hope you’ll see the heart in me 

~ Beautiful Soul by Jesse McCartney ~

What do Beyoncé, Ne-Yo, Jesse McCartney, and prairie voles have in common? They all care about loyalty to their partner.

If you’ve ever been in love or watched a romantic movie, you know of the bond two people can share. It is a strong attachment and a commitment to choose your person over anyone else. 

Several animals show this type of bond and social attachment. From penguins to eagles to humans, many animals mate for life. One animal that exhibits life-long mating and partner bonding is the prairie vole. The prairie vole, which is also relatively easy to collect and contain, has therefore been used by scientists to study these social behaviors. 

Social behaviors, and behaviors in general, are controlled by the brain. The brain and its many cells are influenced by certain molecules. One molecule important for social behavior is oxytocin. Since the late 1900s, oxytocin has been widely recognized for its role in social bonding and attachment in both human and non-human species (including prairie voles). Oxytocin, through the oxytocin receptor, acts in behaviors such as social attachment, childbirth, and caring for children.

However, the ways in which genes influence these behaviors has been more difficult to discover. The organisms used for these genetic studies (e.g. fruit flies, mice) do not exhibit these social behaviors. This study aims to address that issue by using a powerful genetic technique in an organism that exhibits the social behaviors of interest (i.e. the prairie vole). 

Kristen Berendzen and colleagues investigated whether or not the oxytocin receptor (OXTR), through which oxytocin acts, is necessary for pair bonding, parental behavior, nursing, or childbirth in prairie voles. The authors used Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), a genetic technique used to delete segments of DNA, to mutate the OXTR in prairie voles. Through this strategy, three groups of prairie vole OXTR mutations were created. Each of these mutations caused the OXTR not to work properly and therefore oxytocin could not act through it.  

Once these three groups of prairie voles were created, the authors tested whether these OXTR mutations caused changes in the behaviors related to the oxytocin system: pair bonding (when the vole prefers their partner over another vole), parental care, birth of young pups, and survival of young pups.

They found that prairie voles within each of the three OXTR-mutant groups showed preference for their partners (pair bonding) and parental care for their pups. While some pups born of the OXTR-mutants did survive, certain mutant groups showed significantly fewer surviving pups and those that survived weighed less. Additionally, while maternal care seemed relatively normal, there was a mutant group that exhibited a deficit in paternal care. From this, the authors concluded that the OXTR and OXTR-mediated signaling are not required for pair-bonding, nursing, or pup-rearing behaviors, but that there might be some variation in how the mutation impacted other behaviors like maternal milk production and paternal care.

While this is an exciting and shocking finding, it is important to consider that something else might be going on. It is possible that another system, known as the vasopressin system, is compensating for the oxytocin system. Since vasopressin and oxytocin are involved in similar roles, it is possible that the mutation of the OXTR caused components of the vasopressin system to come in and help accomplish the behaviors. It will be important to look into this more deeply in the future.

This study questions decades of oxytocin system research. What is the balance between doing something that shocks the field and trusting previous research? Is there a future where advances in technology lead to disproving years of research? It is crucial these results are repeated, and it will be interesting to see where oxytocin/vasopressin research goes from here.

Though this paper claimed the oxytocin receptor is not necessary for multiple social behaviors in prairie voles, that does not mean the oxytocin system can be completely ruled out for involvement in such behaviors. Much more needs to be done to uncover the mechanism behind these behaviors. Until then, the oxytocin system isn’t out of the picture, and love will carry on.

Figure 1. Prairie voles lacking the oxytocin receptor demonstrate intact pair bonding, childbirth, and parenting behaviors. They also show partially intact nursing behaviors.

Edited by Gabriella Muwanga.

REFERENCES

Berendzen, Kristen M., et al. "Oxytocin receptor is not required for social attachment in prairie voles." Neuron 111.6 (2023): 787-796.