The internal structure of axons from rat sciatic nerve.

Area of Science:

• Neuroscience
• Cell Biology
• Electron Microscopy

Background:

• Intra-axonal organelles and their structural organization are critical for neuronal function.
• Microtubules play a vital role in maintaining neuronal structure and transport.
• The precise composition and interactions of filamentous networks within axons remain incompletely understood.

Purpose of the Study:

• To investigate the ultrastructure of the intra-axonal filamentous network in rat sciatic nerves.
• To determine the relationship between this filamentous network and microtubules under varying conditions.
• To elucidate the dynamic nature of axonal structural components.

Main Methods:

• Rat sciatic nerves were fixed using a combination of glutaraldehyde and tannic acid.
• Electron microscopy was employed to visualize the intra-axonal filamentous network.
• Nerve samples were subjected to cold exposure and subsequent incubation at 37°C, with and without D2O, to assess structural responses.

Main Results:

• A filamentous network, comprising 10 nm longitudinal filaments and 6 nm cross-linking filaments, was identified between intra-axonal organelles.
• Cold exposure disrupted microtubules but not the filaments; subsequent warming led to microtubule reformation and re-linking with filaments.
• Exposure to cold in the presence of D2O prevented microtubule disruption but caused some loss of fine filaments.

Conclusions:

• The study reveals a distinct filamentous network within axons, separate from microtubules.
• A dynamic relationship exists between the identified filaments and microtubules, evidenced by their interaction during reformation after disruption.
• The findings suggest that the cross-linking filaments differ in nature from the longitudinal filaments and are involved in microtubule stability and dynamics.