Chena River Fish May Hold Evolutionary Clues to Breathing Origins
Fairbanks, AK - Elections, stormy weather, the impending winter darkness.... we all need to take a deep breath this time of year. Luckily, our bodies can’t forget to breathe. But we have all forgotten when and how breathing began. Now, scientists at the University of Alaska Fairbanks may have discovered the origins of the process. The answer comes from a primitive fish that still swims Alaska's rivers.
The constant drone of a large cooler hums in the corner of Michael Harris’s lab at the University of Alaska, Fairbanks. Harris is a Respiratory Neuro Biologist. He’s keeping tiny, juvenile lamprey in that cooler and he’s convinced they hold the secret to the evolution of air breathing in humans.
“At rest right now standing here, we actually breathe in order to get rid of carbon dioxide that we produce through metabolism," Harris explains. "And if we do that effectively we can’t help to get all the oxygen we need," he says.
Harris says our bodies know when and how to expel carbon dioxide because of sensors in our brains. But he doesn’t know when humans developed those sensors. That’s what the lamprey are for. They’re an extremely primitive fish. They don’t breathe air, but they do use gills to take in oxygen. Harris decided to look at lamprey brains up close to find out if they were also sensitive to carbon dioxide. “It certainly does have the aura of science fiction," he smiles. "So, the old movie depictions of the brains kept alive in the jar of saline. That is actually what we do and it does actually work.”
With the help of Lab Technician, Megan Hoffman, Harris exposed nerves in the lamprey brains to different concentrations of the gas. The result was nerve activity that is typically associated with breathing. Harris believes it’s the kind of activity that eventually led air-breathing animals to cough in response to bad air, or in this case, lots of carbon dioxide.
“When we induced a cough for the first time with carbon dioxide, I think we both laughed hysterically," says Harris.
Megan Hoffman says she laughed too. "It was just exciting to see it working. Especially when we stimulated it more with CO2 that was particularly exciting."
Now, part of the reason Harris and Hoffman laugh is because what they consider a lamprey “cough” really looks funny. After testing brains, Harris tried the same experiment with a live lamprey.
There’s a small aquarium, with about two inches of water in the lab. A long, skinny, pink and brown lamprey rests in a glass tube under the water. A microscope projects a video as Harris exposes the lamprey to carbon dioxide. "It does look like he coughed, it really does," laughs Harris.
The lamprey undulates from front to back, as if it has the hiccups, and the water moves in a wave out of the tube. These fish spend their first five years in burrows they dig into the bottom of riverbeds throughout Interior Alaska. Carbon dioxide builds up in those burrows as the lamprey sit and filter feed.
“What we think then is that the build-up of CO2 in the water in the ecluded tunnel stimulates a response in the animals to cough," explains Harris. "And when they cough, they expel water from their pharynx back out the front of their body, which would make a water current in the tunnel that would blow the mud out of the eclusion.”
Harris collaborates with Neuro Scientist Barbara Taylor. She says the simplicity of this experiment is what makes the findings so exciting. “We strive for that!" say Taylor. "Yeah, when it’s elegantly simple, that’s when you can think you’re really on to something.”
Both Taylor and Harris are interested in finding out more about how different pathologies like Central Sleep Apnea, Sudden Infant Death Syndrome and Retts syndrome developed as animals evolved to breathe air. “So, if we can understand that how lamprey control cough is generated by the same types of neurons," say Harris, "the neurons that are some important to humans that when they fail, breathing fails, we can understand what are critical elements and what are peripheral elements that are secondary to the critical system.”
Harris is halfway through experiments with live lamprey. He presented his research at the annual Society for Neuroscience in New Orleans earlier this month. He says he was so excited about the response that he wrote up a manuscript for publication on his flight back home. He hopes to have his results published within the next few months.