A groundbreaking study reveals that the signaling components of neurons may not be as smooth as previously thought, but rather a series of irregularly shaped blobs.
The Message-Sending Part of Neurons May Be Blobby, Not Smooth
A new study has added some flourishes to the classical picture of nerve fibers called axons. Like a garland of cranberries hung on a Christmas tree, these ultrathin tendrils that zip messages around the nervous system may actually be a series of bumps.
Physicists have known about this sort of “pearls-on-a-string” shape for a long time. Thin strands of fluids form beads when stretched, a phenomenon that can be spotted in viscous fluids like honey and aloe vera gel. Beads have also been spotted on axons, which are in some ways like those liquids, with malleable internal and external parts.
A New Way of Seeing Axons
To see axons as they truly are, researchers used a high-pressure freezing method instead of the common chemicals that preserve or “fix” cells. This sort of cryopreservation is like making a frozen grape, says Shigeki Watanabe, a cell biologist and neuroscientist at Johns Hopkins University School of Medicine.
The frozen mouse axons were made of rotund blobs connected by thin tubes, electron microscope images revealed. The researchers did the experiments with a type of axon that isn’t wrapped in insulating material called myelin. Further unpublished experiments show a similar “pearls-on-a-string” structure on myelinated axons, Watanabe says.
The Shape of Axons
These blobs — formally known as nanoscopic varicosities — form because of physical mechanics, Watanabe says. It takes less energy to make the blob structure than it does to make a cylinder, he says. An axon’s shape influences how fast signals move along it, modeling experiments and experiments in mice axons suggest.
But the matter isn’t settled. The freezing method could be distorting the axons somehow. “It’s possible that the technique is not there yet, to actually see things properly,” Watanabe says. “But I feel confident about what we observe.”
What’s Next?
Watanabe and colleagues plan to study whether pearled axons are affected by sleep, a time when the mechanical environment changes in the brain. They’re also eager to study the shapes more by looking at axons inside living brains.
- sciencenews.org | The message sending part of neurons may be blobby, not smooth
