Prairie voles have long been heralded as models of monogamy. Now a study suggests that the “love hormone” once thought essential for bonding – oxytocin – may not be so necessary after all.
Interest in the romantic life of prairie voles (Microtus ochrogaster) for the first time more than 40 years ago, says Devanand Manoli, a biologist at the University of California, San Francisco. Biologists wanting to capture flies for study often want to capture two at a time because “what they’re finding are these male pairs,” he says. Unlike many other mice, the voles of the meadow, it turns out, come together for life with their myriad companions.SN: 10/5/15).
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Paired voles primarily prefer the companionship of strangers and similar encounters both in the wild and in the lab. Because other species of vole do not have complex social behavior like the common vole, it is a popular animal system for studying how social behavior evolves.
Research over the past few decades has implicated a few hormones in the brain that are vital to specific flight behaviors, most notably oxytocin, which is also important for social behavior in humans and other animals.
Manoli and colleagues found the oxytocin receptor, a protein that detects and reacts to oxytocin, would be the perfect test for a new genetic engineering method based on the CRISPR technique, which uses molecules from bacteria to selectively turn off genes. Researchers have used techniques in vole embryos to create animals born without oxytocin receptors. The team figured out that the mice couldn’t form bonds — like flies in past experiments whose activity was blocked by the drug oxytocin.
But, Manoli said, the researchers got “a big surprise.” Birds were able to form bonds even without oxytocin, the team reports on March 15 Neurons.
“I was very surprised by their results,” says Larry Young, a biologist at Emory University in Atlanta, who was not involved in the study but has studied oxytocin’s role in sexual dysfunction for decades.
The main difference between the new study and past studies that used drugs for oxytocin is the exact timing when the hormone’s activity is suppressed. With the drugs, the adult flies released oxytocin in their brains before shutoff. With CRISPR, “these animals never experience oxytocin signaling in the brain,” says Young, whose research group recently replicated Manoli’s experiment and found the same result.
Perhaps, he says, when young, pair bonding is controlled by a brain circuit that typically becomes dependent on oxytocin through exposure to it during development, like a symphony orchestrated by a conductor. Suddenly, that conductor and the symphony will sound absent, with a band of Yadria that never performs with a conductor worth so much.
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Manoli agrees to be artistic in matters of timing. A second reason for the disparity, he says, could be that drugs often have off-target effects, so that chemicals meant to block oxytocin could be affecting other things in the brain that lead to mating. But the young man disagreed. “I don’t believe it,” he said. “the” [drug] the use of that population is very selective, “not even binding to the receptor of oxytocin’s closest molecular relative, vasopressin”.
Does this mean that decades of past work are hung in the balance? Not silent.
“It shows that this problem is much more complicated,” Manoli said. “The pharmacologic manipulations … suggested” [oxytocin] plays a critical role. The question is, what is this role?
The new results make stunning sense if you look at the big picture, Manoli says. The ability to pair bonds is “just as critical to the survival of the species,” he says. “From a genetics perspective, it can make sense that there is no single point of failure.”
The group now hopes to look at how other hormones, such as vasopressin, influence mating using this relatively new genetic technique. They are also looking more closely at the behavior of the flies to make sure that CRISPR gene editing doesn’t change it in a way that hasn’t been noticed yet.
The flight of “love” in the game looks like all of us players are still trying to understand.
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