Scientists at Max Planck Institute for Neurobiology create transparent spinal cord imaging

Scientists at the Max Planck Institute for Neurobiology have devised a new technique to create a three-dimensional model image of spinal tissue.

Nerve cells in the spinal cord are responsible for connecting the brain to the peripheral nervous system, which is made up of the somatic and the autonomic nervous system. These systems are responsible for coordination, external stimuli processes, and functions humans have no conscious control over. Damage to the spinal cord can thus have debilitating and irreversible effects such as paralysis.

Despite years of extensive research, scientists have struggled to find a way to stimulate damaged nerve cell filaments to regenerate growth, which usually occurs only millimeters at a time, if at all.  

One of the techniques used by scientists to record the process of regeneration has been to cut the observed nerve into thin slices and observe them under a microscope. The flaw with this method is that mistakes are almost guaranteed; scientists could accidentally squish the nerve cell while slicing or they could unintentionally misalign the layers while stacking, thereby affecting the accuracy of the data. In some cases, if scientists wanted a somewhat three-dimensional image, each slice was digitalized and put together like a puzzle.  "Although this might not seem dramatic to begin with it prevents us from establishing the length and extent of growth of single cells," said Frank Bradke.

Given the time-consuming nature of this approach and the lack of cellular resolution in computed tomography scans (CT scans) and magnetic resonance imaging (MRI), scientists were desperate for a more reasonable technique to track regeneration.

Scientist Hans Ulrich Dodt made progress in damage assessment when he improved on the technique of ultramicroscopy. Dodt advanced an older ultramicroscope method (created in 1913) and was able to create an image with high resolution, but still, it was not enough.

Now, as scientists at the Max Planck Institute for Neurobiology announced on Christmas Day, they have innovated imaging techniques by making the spinal cord transparent.

Naturally, the spinal cord tissue, made up of water and protein, is opaque due to differences in water and protein light refraction. In order to make the tissue transparent, scientists removed the water from the tissue under examination and replaced it with a medium that refracts light in the same way as proteins do. Because the proteins and the mediums uniformly refract light, the result was an absolutely transparent piece of tissue suitable for imaging observation.

"It's the same effect as if you were to spread honey onto textured glass", Ali Ertürk, the study's first author adds. Once the honey is spread and compensated for the irregularities on the surface, the opaque pane becomes crystal clear.

Scientists can use fluorescent-staining dyes on individual nerve cells on a transparent section of spinal cord to trace the path from all possible ‘angles’ in an otherwise transparent cord section. Observing the dye reveals whether or not nerve cells actually continue to grown after substantial injury.

According to the Max Planck Institute, this is a breakthrough technique in regeneration research. "The really great thing is the fact that this method can also be easily applied to other kinds of tissue," Frank Bradke pointed out.