Protein transport between crayfish lateral giant axons.

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Segmental lateral giant axons (SLGAs) in crayfish provide a model for studying axonal transport.
• Understanding protein movement between neurons is crucial for neural plasticity and repair.

Purpose of the Study:

• To investigate if functionally intact proteins can move between adjacent axons under physiological conditions.
• To elucidate the mechanism of axon-to-axon protein transport.

Main Methods:

• Iontophoretic injection of horseradish peroxidase (HRP) into single SLGAs in crayfish.
• Localization of HRP using a non-cytotoxic procedure requiring intact enzymatic activity.
• Analysis of HRP localization in adjacent SLGAs and associated structures.
• Assessment of HRP transfer under varying calcium concentrations and measurement of synaptic electrical resistance.

Main Results:

• Horseradish peroxidase (HRP) frequently transferred between injected and adjacent SLGAs.
• HRP transfer occurred more frequently in the caudal direction than rostral.
• Ultrastructural analysis revealed HRP associated with vesicles at septate junctions and in the perijunctional extracellular space.
• HRP transfer was significantly reduced in low-calcium saline, suggesting a calcium-dependent mechanism.
• No difference in synaptic electrical resistance was observed between sites with and without HRP transfer.

Conclusions:

• Axon-to-axon protein transport occurs via exocytosis from the injected axon and endocytosis by the adjacent axon.
• This mechanism is calcium-dependent and involves vesicular transport across septate junctions.
• Such protein transfer may contribute to the long-term survival of severed axon segments.