Treating young mice who display symptoms of autism with oxytocin, a hormone involved in human bonding, improves their social behavior for as much as a week, according to a study published in Science Translational Medicine today. The finding, the researchers say, could one day lead to human treatments. But in the meantime, the study hints that scientists need to investigate oxytocin levels in humans to find out which type of autism spectrum disorder, if any, would be most likely to benefit from an eventual oxytocin-based drug.
"We are able to improve social behavior using oxytocin"
About 1 in 68 children have some form of autism spectrum disorder, according to the CDC, and it’s about five times more common in boys. There is no cure for autism, and the disorder is costly: taking care of a child with autism spectrum disorder costs about $17,000 more per year than caring for a child without it, the CDC says. That estimate includes services like therapy, education, and caregiver time — all aspects of a child’s life that could benefit from a treatment that improves the way a child interacts with other human beings.
In the study, researchers investigated the effects of oxytocin on adult and juvenile mice who have been genetically modified to display symptoms of autism. Oxytocin improved the social behavior of both groups: the treated mice were more likely to choose interacting with another mouse over inspecting an inanimate object compared with mice who hadn’t been treated with oxytocin. But the effects only lasted a few hours in the adults. The juveniles remained more social for about a week after stopping the treatment. The researchers obtained the same results when they gave the mice a drug that triggers the natural release of oxytocin in the brain.
There might be a critical period in which you can jumpstart the natural release of oxytocin in the brain
"We are able to improve social behavior using oxytocin in a mouse model of autism, and in general the effect lasts a couple of hours," says Daniel Geschwind, a neurologist at The University of California, Los Angeles, and a co-author of the study. "However, if you treat the animals early, it seems that there can be a longer-lasting effect." This suggests that there might be a critical period in which you can jumpstart the natural release of oxytocin in the brain. Unfortunately, Geshwind says, the researchers don’t know yet if the longer effect lasts when the mice get older. This is something that they hope to look at next.
Richard Tsien, a neuroscientist at New York University who didn’t participate in the study, says that he was impressed that the approach had such "a big effect — a doubling of social interaction time." This means that cells that release oxytocin and the circuits that respond to oxytocin are basically working, he says, even in the mouse model of autism — they just need a boost. "It's not an absolute failure of development as some might have predicted."
the "love hormone" increases envy and decreases cooperation in humans
This is just the first of many studies, Geschwin says. "We need to refine our understanding of when the optimal dose is to give the long-lasting effect." But even if the researchers find out more about oxytocin's effect on mice, it’s still possible that the results will fail to translate to humans. "Until one uses the mouse data to develop a therapy that is successful in humans," he says, "it’s impossible [to know] with certainty."
If oxytocin does end up being helpful in humans, however, it’s likely that it will only work for some forms of autism spectrum disorder. Oxytocin has been referred to as "the love hormone" in the past, but previous studies have found that it may also increase envy and decrease cooperation in humans, in addition to facilitating social bonding. This means that it’s likely that the circumstance in which the drug is given to humans — as well as the sex and age of the recipient — might be important in determining its effects. "That’s why my sense is that the best way to start with human trials of oxytocin is to target those with known oxytocin defects," a defect that has actually yet to be identified in autism, Geschwin says.
"While much work remains to be done to understand [the findings]," Tsien says, "this is a terrific start."