Long-lasting increase in axonal excitability after epidurally applied DC.

Area of Science:

• Neuroscience
• Physiology

Background:

• Direct current (DC) effects on nerve fibers are typically studied during or immediately after application.
• Recent findings show cathodal DC increases excitability of intraspinal axonal branches for extended periods.

Purpose of the Study:

• To investigate if DC induces a similar long-lasting excitability increase in myelinated axons of the dorsal columns.
• To explore the potential of combining DC polarization with epidural stimulation for therapeutic benefits.

Main Methods:

• Epidural stimulation of dorsal column fibers in anesthetized rats.
• Monitoring compound action potentials in peripheral nerves to assess fiber excitability.
• Applying low-intensity cathodal DC polarization (0.8-1.0 µA).

Main Results:

• Cathodal polarization increased the number of activated epidural fibers severalfold.
• The excitability enhancement occurred within seconds and persisted for over an hour.
• The observed plasticity was activity-independent, not requiring concurrent fiber stimulation.

Conclusions:

• DC polarization induces a novel, long-lasting plasticity in myelinated dorsal column fibers.
• This plasticity is distinct from that observed in preterminal axonal branches, suggesting different mechanisms.
• Combining transspinal DC polarization with epidural stimulation may significantly improve therapeutic outcomes for pain and motor function.