Quantitative objective assessment of peripheral nociceptive C fibre function

Area of Science:

• Neuroscience
• Physiology
• Dermatology

Background:

• Peripheral nociceptive C fibres play a crucial role in pain and sensory perception.
• Assessing C fibre function is vital for diagnosing neuropathies and understanding pain mechanisms.
• Current methods for evaluating C fibre function can be invasive or lack quantitative precision.

Purpose of the Study:

• To develop and validate a novel technique for the quantitative assessment of peripheral nociceptive C fibre function.
• To investigate the neurogenic vasodilatation response (axon reflex flare) induced by acetylcholine.
• To compare acetylcholine-induced flare with other forms of cutaneous vasodilation.

Main Methods:

• A technique utilizing acetylcholine electrophoresis to stimulate C fibre endings and measure axon reflex flare.
• Laser Doppler flowmetry was employed to quantify the increase in blood flow within the flare area.
• The neurogenic flare was compared to mechanically or chemically induced non-neurogenic vasodilation and tested for abolition by local anaesthetics.

Main Results:

• The acetylcholine-induced axon reflex flare is a reliable indicator of neurogenic vasodilatation.
• The flare response was abolished by local anaesthetics, confirming its neurogenic origin.
• In 96 healthy subjects, the size of the axon reflex flare on the sole of the foot showed a significant decrease with increasing age in males, but not in females.

Conclusions:

• The described technique provides a quantitative and reliable method for assessing peripheral nociceptive C fibre function.
• Age-related decline in C fibre function, specifically neurogenic vasodilation, is evident in males but not females.
• This method holds potential for clinical applications in diagnosing and monitoring conditions affecting C fibre function.