Visualizing the Synaptic and Cellular Ultrastructure in Neurons Differentiated from Human Induced Neural Stem...

Area of Science:

• Neuroscience
• Cell Biology
• Microscopy

Background:

• Synaptic subcomponents are below the resolution limits of light microscopy.
• Transmission electron microscopy (TEM) offers unparalleled resolution for ultrastructural analysis.
• Human postmortem tissue often lacks adequate quality for high-resolution TEM, necessitating alternative sample preparation methods.

Purpose of the Study:

• To identify optimal culture, embedding, and staining techniques for superior ultrastructural preservation of human neurons.
• To enable detailed visualization of neuronal elements, particularly synaptic structures, using TEM.

Main Methods:

• Two induced neural stem cell lines were differentiated into neurons using three culture methods: adherent on glass coverslips, embedded in Matrigel, or as compact free-floating neurospheres.
• Samples underwent fixation with glutaraldehyde (GA) and paraformaldehyde (PFA).
• Three staining protocols were applied: standard stain, Ruthenium red stain, and high-contrast en-bloc stain, followed by TEM imaging.

Main Results:

• Compact free-floating neurospheres demonstrated the best overall ultrastructural preservation.
• The high-contrast en-bloc stain provided exceptionally sharp membrane visualization and the highest quality imaging of neuronal structures.
• This combined approach significantly improved the visualization of membrane structures essential for synaptic analysis.

Conclusions:

• Compact neurospheres cultured under free-floating conditions yield optimal ultrastructural preservation.
• A high-contrast en-bloc staining protocol is recommended for superior visualization of neuronal membrane structures.
• This optimized protocol is ideal for detailed analysis of synaptic structures using TEM.