Oxytocin nose drops may spice up marmoset relationships, deepening the bond from both sides, even when only one monkey is given the hormone.
The hormone oxytocin is released when humans are in love, be it with a partner or a child, winning it the nickname of the “love molecule,” although it has a dark side as well.
Numerous experiments have explored the effects of administering oxytocin to animals, showing it makes both adults and infants more social and reduces tendencies to stray. These studies, however, have only examined how receiving oxyctocin alters the behavior of the recipient.
Now, a paper published in Frontiers in Behavioral Neuroscience looks instead at how monkeys respond when their partners are given oxytocin nasal drops. "We are the first to show that marmosets treated with oxytocin receive more social attention from their long-term mate," said first author Jon Cavanaugh in a statement. Cavanaugh is a graduate student at the University of Nebraska, Omaha.
People feeling neglected by their partners might be premature in sticking oxytocin up their own noses, but Cavanaugh found that when either partner in the pair-bonded species Callithrix Jacchus (common marmosets) was treated with the drops, it changed their mate's behavior.
"We found that untreated marmosets displayed greater interest in interacting with their long-term mate when their mate received oxytocin than when their mate received a placebo, potentially indicating an increase in perceived social attractiveness,” Cavanaugh said. Unlike some primates, breeding pairs of marmosets spend a lot of time together and this is important to maintaining the bond.
It might be expected that the untreated mate's reaction would be in response to treated individuals becoming more sexual or cuddly. However, Cavanaugh said, “The changes induced by oxytocin seem exceptionally subtle, since we did not observe any obvious difference in the solicitation behavior of the oxytocin-treated marmoset." Nor did treated monkeys, male or female, have more sex during the observation period.
Exactly what cues the treated individuals put out to alter the behavior of their partner remains unclear, but something worked. Male marmosets spent more time grooming their dosed up paramours, while females whose partners had been given the drug responded by spending more time physically close to the recipient.
The study was done on just six marmoset couples, and the observations lasted only 20 minutes, making the results very preliminary, although all the findings comfortably met statistical significance, particularly the extra grooming of the female oxytocin recipients.
Co-author Professor Jeffrey French argued that, “Further exploration of how oxytocin may modify the attractiveness of social partners could identify another mechanism by which this molecule can help with disorders that have social dysfunction as a prominent feature.”
The authors argue that the marmoset's flexible relationships makes it a good model for humans, and note that, “Relatively little is known about the neuroendocrine underpinnings of maintaining [long-term relationships]” in any species. Consequently, the research could be an entry point to further investigations of the way hormones affect long-term relationships.
