Is cold paresis related to axonal depolarization?

Area of Science:

• Neuroscience
• Physiology

Background:

• Cold paresis, observed in conditions like multifocal motor neuropathy, is hypothesized to result from axonal depolarization due to impaired Na/K-pump activity.
• Cooling may exacerbate this by further reducing pump function, leading to conduction block and weakness, but direct evidence in human motor axons is lacking.

Purpose of the Study:

• To investigate whether cooling induces axonal depolarization in human motor axons.
• To explore the underlying mechanisms of cold-induced weakness, including effects on nerve function and muscle contraction.

Main Methods:

• Ten healthy subjects were tested at various temperatures (37°C down to 15°C).
• Nerve excitability, nerve conduction (decrement tests), arterial blood flow (Doppler), and muscle strength were assessed.

Main Results:

• Cooling induced changes in nerve excitability consistent with axonal depolarization.
• Reduced nerve excitability findings included fanning-in of threshold electrotonus and increased refractory period.
• Muscle strength decreased, and relaxation was impaired, though nerve conduction tests remained normal.

Conclusions:

• Cooling demonstrably causes axonal depolarization in human motor nerves, primarily due to temperature-dependent effects on Na/K-pump activity.
• The observed weakness is likely a combination of nerve depolarization and direct effects on muscle contraction.