Why studying autism in mice may be doomed to fail

Post Reply New Topic

The ideal ‘autism mouse,’ researchers thought at the time, should show all the same traits that characterize autism in people: language and social problems, and restricted and repetitive behaviors. Some mutant mice make fewer ultrasonic vocalizations than controls do, which many behaviorists took to be an analog of language problems. Other models groom, jump or bury marbles to an excessive degree — actions the researchers interpreted as repetitive behaviors reminiscent of autism. But researchers were most intent on sniffing out social deficits, a hallmark feature of autism. If they could pin down a murine model of this trait, the thinking went, perhaps they could design drugs to address it — or could at least better understand the brain pathways involved.

In this test, researchers place a mouse in a Plexiglas box containing three rooms laid out in a row, and the rodent faces a simple choice: It can spend time in the first room, where another mouse sits imprisoned in a small wire cage, or it can loiter in a back room, which holds an identical but empty cage. Most mice gravitate toward the playmate. But the SHANK3 visitors moved slowly, pausing frequently to groom. (They groom so compulsively, in fact, that they have bald spots where they’ve licked the fur away.) They sometimes sniffed the empty cage and sometimes the other mouse, showing no real preference for the mouse.

Or at least that’s what the 2011 study found. Last year, Silverman and her colleagues published a study looking at two male and two female groups of the same mice in the three-chambered assay, and found something different. This time, the mice showed behavior that was “mostly normal,” the team wrote, with only one group of male mice displaying social deficits in the three-chambered assay. Around the same time, another team also announced that it was unable to replicate the original results. The upshot: Any social deficits in the SHANK3 mice are, at best, significantly milder than previously reported

The excitement over mouse models has since fizzled. Many of the original reports of social deficits in mice have not held up when tested by independent labs — including Silverman’s — or in different strains of mice. Inconsistent findings have plagued studies not just of SHANK3 mice, but also those with mutations in the risk genes CHD8, NLGN3, NLGN4 and CNTNAP2, among others. That has left many scientists wondering whether mice can ever recapitulate something as complex and human as autism.

“I think that defining an autism mouse is folly,” says Valerie Bolivar, director of the Mouse Behavioral Phenotype Analysis Core at the Wadsworth Center in Albany, New York. “To get all those things in a nice, neat package with a bow — we’re just not going to get that.”

Perhaps the biggest problem with using mice to study social skills is that mice aren’t especially social to begin with. The region of the mammalian brain that dictates most social behaviors, the prefrontal cortex, is significantly smaller in mice than in people. In the wild, male mice are highly solitary and may come into contact only with a mate and its pups, says Mu Yang, who directs a mouse behavioral facility at Columbia University. “‘Let me sit next to you; what’s going on?’ That’s not necessarily what mice do.”

Caroline Blanchard, a rodent behaviorist at the University of Sao Paulo in Brazil, has spent nearly 40 years scrutinizing mice as they go about their business in large enclosures that closely mimic their natural habitat. “They are not solitary in the sense that they kill each other if they come too close or something,” says Blanchard. But, she says, “they’re not nearly as social as most rats.”

Rats and monkeys are often hailed as better models for autism research, but support for mice remains strong despite the drawbacks. “Whether the brains of mice and the behavioral repertoires of mice are sophisticated enough to sufficiently monitor autism and its primary symptoms — that, I think, is a very logical question to ask,” Crawley says. “I think about this all the time, and I don’t have an answer“

he fact that many behaviorists are rethinking whether mice can mimic social deficits at all is far from obvious from the literature. Top journals continue to publish studies detailing social deficits in autism mice, often based on inexpert interpretations of the three-chambered assay. “It is annoying when you see the words ‘autism model’ in the title of five Nature papers,” Silverman says.

Researchers often feel pressure from journal reviewers to demonstrate that an autism mouse has social deficits that seem to recapitulate autism, says Guoping Feng, professor of brain and cognitive sciences at the Massachusetts Institute of Technology. Feng led the 2011 study that first showed social deficits in SHANK3 mice. He was mainly interested in looking at the effects of a mutation in SHANK3 on the brain. But for these experiments to be considered meaningful, he understood that the mice needed to show autism-like behaviors.

In 2014, that same pressure drove at least five other teams to look at social behavior in mice with mutations in CHD8, which was emerging as a top candidate gene for autism. By 2016, one team had announced in Nature that they had a CHD8 model showing “autistic-like phenotypes,” even though those mice prefer a playmate to an object in the three-chambered assay.

At the time, Silverman and her collaborators were characterizing a mouse with another mutation in CHD8. Although the findings from both teams were similar, Silverman’s team interpreted the mice as not having any social problems. However, the journals the team approached were hesitant to publish results that seemingly contradicted the other group’s paper. To convince the reviewers, Silverman’s team needed to replicate their behavioral experiments — six months’ worth of work — before they were able to publish.

“This is an example of what’s been happening in the literature with mouse models of autism,” Crawley says. “The first paper that comes out has incorrectly interpreted their findings or done the wrong experiment sometimes, and their findings get popularized in the community and sometimes in the press — and then the next papers that come out that have done things right get lost in the shuffle.” To break this cycle, researchers should work with mouse behaviorists to help interpret their studies, Crawley says.

An even more effective solution might be to move away from the pressure to show autism features altogether, some researchers say. “We need to loosen the standard of framing mouse models using the mouse version of [a diagnostic manual]. When that happens, people can stop trying too hard to shape their data to look like the cardinal symptoms of autism,” Yang says.

The key to truly understanding behavior may be to slow down and chart it manually. Bolivar trained with a scientist who learned animal behavior from zoologist Robert Hinde, who mentored legendary primatologists Jane Goodall and Dian Fossey. This makes Bolivar a “dinosaur,” she says, but also well equipped to study the behavior of a species that is different from people.

Even then, scientists are inferring intent when they decide, for example, that sniffing a nose is a social act. “I have probably scored more social interactions than anybody on earth,” says Yang, who got her start in science 12 years ago testing the first autism mouse models for social deficits. “I scored this nose-to-butt sniffing for 10 years, but do I really understand [it]?”

Probably because they think it’s an acceptable price to pay for one day “curing” autism in humans, meaning there won’t be autistic people freely roaming the paths of the world. And this would certainly be a good thing, amirite?

As you please, but I don't know what the disagrement is about. My last sentence was ironic.

As you please, but I don't know what the disagrement is about. My last sentence was ironic.

No problem. I guess I was a bit overconfident about the clarifying power of a trailing amirite?

Why studying autism in mice may be doomed to fail