Feasibility study on mouse live imaging after spinal cord injury and poly(lactide-co-glycolide) bridge implantation

J. Biomed. Opt., 2018 · DOI: 10.1117/1.JBO.23.6.065007 · Published: June 29, 2018

Spinal Cord Injury Medical Imaging Biomedical

Simple Explanation

This study explores the potential of using live imaging techniques to observe nerve fiber regeneration in mice after spinal cord injury (SCI). A poly(lactide-co-glycolide) (PLG) bridge was implanted to aid regeneration. The researchers used a special type of mouse that expresses a green fluorescent protein (eGFP) in their nerve fibers, allowing for visualization using microscopy. They then observed the nerve fibers as they grew into and through the PLG bridge. They also attempted to visualize the myelination of these regenerated axons using third-harmonic generation (THG) imaging, a label-free technique for detecting myelin. While nerve fiber regrowth was observed, myelination within the bridge could not be detected.

Study Duration

12 weeks

Participants

3 Thy1-eGFP mice

Evidence Level

Not specified

Key Findings

1
Live imaging of neuronal fibers in the spinal cord of Thy1-eGFP mice is feasible both before and after SCI and PLG bridge implantation.
2
Regenerating neuronal fibers were observed accumulating at the rostral entrance of the PLG bridge and some fibers were found to enter the bridge channels.
3
Third-harmonic generation (THG) signal, indicative of myelination, was detected in the rostral parenchyma adjacent to the bridge, but not within the bridge itself.

Research Summary

This feasibility study investigated the use of live imaging to visualize neuronal fiber regeneration after spinal cord injury (SCI) and poly(lactide-co-glycolide) (PLG) bridge implantation in mice. Thy1-eGFP mice, expressing green fluorescent protein in their nerve fibers, were used to facilitate visualization of axonal regrowth. The researchers were able to image neuronal fibers before and after SCI, observing fibers accumulating at the bridge entrance and some entering the bridge channels. While third-harmonic generation (THG) imaging successfully detected myelin in the surrounding tissue, it failed to detect myelination within the PLG bridge, suggesting that myelination may occur later or be inhibited by the bridge environment.

Practical Implications

Improved understanding of SCI regeneration

In vivo imaging can improve our understanding of axonal regeneration and sprouting in the spared parenchyma of the spinal cord after injury.

Tool for assessing therapies

The described imaging approach can serve as a tool to assess therapies aimed at spurring neuronal fiber growth after SCI.

Understanding Myelination dynamics

Combining live imaging of neuronal regrowth with ex vivo determination of myelination status helps understand the dynamics of myelination after SCI.

Study Limitations

1
The study only observed a limited number of fibers entering the bridge at the observed timepoint in the Thy1 model.
2
THG signal was not detected within the bridge, which could be due to the timing of myelination, the properties of the bridge, or limitations of the THG technique.
3
Assessing the level of axonal myelination in vivo is a challenging task because the third-harmonic signal is easily absorbed from the tissues.

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