New study shows that axons may resemble ‘strings of pearls’ rather than smooth lines

Recent research has questioned the traditional understanding of axons, the message-carrying fibers of neurons, revealing that these structures may not always be smooth and cylindrical. A study published Dec. 2 in Nature Neuroscience found that axons may resemble strings of pearls rather than uniform lines. The discovery was made by researchers at the Johns Hopkins University School of Medicine using a high-pressure freezing method for imaging axons from the mouse brain.

According to Dr. Shigeki Watanabe, a cell biologist and neuroscientist at Johns Hopkins, traditional preservation techniques often alter the shape of tissues, leading to discrepancies in observations. According to a report in ScienceNews, they explained that the freezing method they used better preserved the natural structure, comparing the process to drying grapes instead of turning them into raisins. Electron microscopy revealed rotund blebs connected by thin tubes, a feature that had not been systematically studied before.

Physical mechanics behind axonal pearling

Reportedly, the bead structure of the axon, also known as nanoscopic varicosities, was explained by Watanabe as a result of physical mechanics. Creating this shape requires less energy than maintaining the smooth cylindrical structure. Researchers believe that the size of the axon can affect the speed of signal transmission and vice versa. Preliminary data also suggest that myelinated axons, which are coated in insulating materials, may exhibit similar patterns.

Skepticism and examining the future

Pramod Pullarkat, a physicist at the Raman Research Institute in Bengaluru, expressed caution about these findings. In their statement, they emphasized that although the data is compelling, more evidence is needed to confirm this phenomenon in different situations. They highlighted that axons grown in laboratory settings often appear smooth, which raises questions about whether the observed structures are a subset or an artifact of the imaging process.

Further studies are planned to investigate whether these bead axons are affected by factors such as sleep or other changes in the brain environment. The researchers aim to explore axonal structures in the living brain to verify these findings and understand their broader implications.