Turning
a decades-old dogma on its head, new research shows that the receptor
for oxytocin, a hormone considered essential to forming social bonds,
may not play the critical role that scientists have assigned to it for
the past 30 years.
In the study, appearing in Neuron,
the team found that prairie voles bred without receptors for oxytocin
and showed the same monogamous mating, attachment, and parenting
behaviors as regular voles. In addition, females without oxytocin
receptors gave birth and produced milk, though in smaller quantities,
than ordinary female voles.
The
results indicate that the biology underlying pair bonding and parenting
isn't purely dictated by the receptors for oxytocin, sometimes referred
to as the “love hormone.”
“While
oxytocin has been considered ‘Love Potion #9,’ it seems that potions 1
through 8 might be sufficient,” said a senior author of the paper. “This
study tells us that oxytocin is likely just one part of a much more
complex genetic program.”
Because
prairie voles are one of the few mammalian species known to form
lifelong monogamous relationships, researchers study them to better
understand the biology of social bonding.
Studies
in the 1990s using drugs that prevent oxytocin from binding to its
receptor found that voles were unable to pair bond, giving rise to the
idea that the hormone is essential to forming such attachments.
For
this study, 15 years in the making, the researchers applied new genetic
technologies to confirm if oxytocin binding to its receptor was indeed
the factor behind pair bonding. They used CRISPR to generate prairie
voles that lack functional oxytocin receptors. Then, they tested the
mutant voles to see whether they could form enduring partnerships with
other voles.
To the researchers’ surprise, the mutant voles formed pair bonds just as readily as normal voles.
“The
patterns were indistinguishable,” said the author. “The major
behavioral traits that were thought to be dependent on oxytocin – sexual
partners huddling together and rejecting other potential partners as
well as parenting by mothers and fathers – appear to be completely
intact in the absence of its receptor.”
Even
more surprising than the pair bonding was the fact that a significant
percentage of the female voles were able to give birth and provide milk
for their pups.
Oxytocin
is likely to have a role in both birth and lactation, but one that is
more nuanced than previously thought, the author said. Female voles
without receptors proved perfectly capable of giving birth, on the same
timeframe and in the same way as the regular animals, even though labor
has been thought to rely on oxytocin.
The
results help to clear up some of the mystery surrounding the hormone’s
role in childbirth: Oxytocin is commonly used to induce labor but
blocking its activity in mothers who experience premature labor isn’t
better than other approaches for halting contractions.
When
it came to producing milk and feeding pups, however, the researchers
were taken aback. Oxytocin binding to its receptor has been considered
essential for milk ejection and parental care for many decades, but half
of the mutant females were able to nurse and wean their pups
successfully, indicating that oxytocin signaling plays a role, but it is
less vital than previously thought.
“This overturns
conventional wisdom about lactation and oxytocin that’s existed for a
much longer time than the pair bonding association,” said the other
co-senior author. “It’s a standard in medical textbooks that the milk
letdown reflex is mediated by the hormone, and here we are saying, ‘Wait
a second, there’s more to it than that.’”
The
researchers said their study strongly suggests that the current model –
a single pathway or molecule being responsible for social attachment
–is oversimplified. This conclusion makes sense from an evolutionary
perspective, they said, given the importance of attachment to the
perpetuation of many social species.
“These
behaviors are too important to survival to hinge on this single point
of potential failure,” said the author. “There are likely other pathways
or other genetic wiring to allow for that behavior. Oxytocin receptor
signaling could be one part of that program, but it’s not the be-all
end-all.”
The discovery points the researchers down new paths to improving the lives of people struggling to find social connection.
“If
we can find the key pathway that mediates attachment and bonding
behavior,” the other co-senior author said, “We’ll have an eminently
druggable target for alleviating symptoms in autism, schizophrenia, many
other psychiatric disorders.”
https://www.cell.com/neuron/fulltext/S0896-6273(22)01084-4
http://sciencemission.com/site/index.php?page=news&type=view&id=publications%2Foxytocin-receptor-is&filter=22