Photo: Flickr/John Tann
The smartest of fruit flies couldn't dream up the Hyperloop, use an iPad, or even hang in a civilized debate with a congressman. And they most certainly can't carry a football or an assault rifle. But fruit flies might hold our best chance at finally understanding traumatic brain injury (TBI), a problem that's currently devastating scores of football players, soldiers, and car accident victims.
We know TBI is often caused by concussions, whiplash, or repeated blows to the head. We also know that TBI differs in severity among individuals: Some people may get TBI from a minor impact, while others are able to sustain hundreds of head-to-head hits in football with seemingly little effect. What little we know about TBI has been deduced from analysis of symptoms, brain scans, post-mortem brain dissections, and mouse and rat trials. But neurological research is, by definition, difficult and costly.
That's why it's exciting that an almost forgotten mistake could usher in new experiments.
Forty years ago, University of Wisconsin geneticist Barry Ganetzky was holding a glass vial of fruit flies and slammed it against his other hand. He noticed that many of the flies in the vial were paralyzed by the incident, but were seemingly back to normal soon after.
"They weren't mechanically damaged. After five minutes, they would resume activity," Ganetzky said. "When you think about it, that's kind of what happens in a concussion. You have a temporary incapacitation and then you're seemingly back to normal. I was thinking about this recently and I thought, maybe I already have a model of TBI in fruit flies?"
He recently took those thoughts to a colleague, David Wassarman, and decided to do a more involved study. Wassarman developed the high-impact trauma (HIT) device, a spring loaded gadget that smacks a vial of flies against a pad, allowing the researchers to control for speed and intensity of impact.
Here's what happens to fruit flies when you whack them against a pad. Photo: PNAS
Like humans, fruit flies seemingly have long-term effects from a traumatic injury, and like in humans, these symptoms don't always manifest themselves right away. Their research was published Monday in Proceedings of the National Academy of Sciences.
"A certain percentage will die from the initial injury, like humans in a car accident. Then those that have survived, they have a shortened lifespan, some have behavioral deficits in walking and climbing, others have neurodegeneration—holes in the brain—like what we see in humans," Ganetzky said. "That's what's most exciting about this report. We haven't learned anything novel, but the fact that we can replicate most of the key features of human TBI in flies is quite remarkable."
A fruit fly's brain will never make a good model for human intelligence, but at a purely mechanical and genealogical level, this experiment could open the door for some important findings. A fly's brain is also encased in a hard, skull-like structure.
But the genetics of fruit flies are some of the most-studied of lab animals, and genetic analogs in humans are well known. Because TBI affects individuals with different levels of severity in both humans and flies, Ganetzky says future research can help identify genetic markers that predisposes someone to TBI, which could, for instance, help a parent decide if their child should play football or not.
"It's true that flies are not humans, but when you get down to gene structures and mechanisms, they are often very similar," he said. "They've been used for everything else, complicated diseases like cancer and diabetes, alcoholism, epilepsy, and that sort of thing. Why not TBI?"
If that doesn't work, maybe we can just keep growing brains in test tubes.