New Study Finds Axons May Resemble 'Strings of Beads' Instead of Smooth Lines

Recent research has called into question the traditional understanding of axons, the message-sending fibres of neurons, suggesting that these structures may not always be smooth and cylindrical. A study published on December 2 in Nature Neuroscience observed that axons can resemble strings of beads rather than uniform lines. This discovery was made by researchers at Johns Hopkins University School of Medicine using a high-pressure freezing method for imaging axons from mouse brains.

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. As per a report by ScienceNews, he explained that the freezing method they employed better preserves the natural structure, likening the process to freezing grapes instead of drying them into raisins. Electron microscopy revealed rotund blobs connected by thin tubes, a feature not previously studied systematically.

Physical Mechanics Behind Axonal Pearling

Reportedly, the beaded structure of axons, also known as nanoscopic varicosities, was explained by Watanabe as a result of physical mechanics. Creating this shape requires less energy than maintaining a smooth cylindrical structure. The researchers believe that the shape of axons might influence the speed of signal transmission and vice versa. Preliminary data also suggest that myelinated axons, which are coated in insulating material, may exhibit similar patterns.

Scepticism and Future Investigations

Pramod Pullarkat, a physicist from the Raman Research Institute in Bengaluru, expressed caution regarding these findings. In his statement, he emphasised that while the data is compelling, more evidence is needed to confirm this phenomenon across different conditions. He highlighted that axons grown in laboratory settings often appear smooth, which raises questions about whether the observed structures are a subset or artefacts of the imaging process.

Further studies are planned to investigate whether these beaded axons are influenced by factors such as sleep or other changes in the brain's environment. Researchers aim to explore axonal structures in living brains to verify these findings and understand their broader implications.