Assessment of the neurogenic flare response as a measure of nociceptor C fibre function

Abstract

A modified method for quantitative measurement of nociceptor C fibre function is described. The electrophoresis of acetylcholine stimulates C fibres to produce an axon reflex flare which is measured by laser Doppler flowmetry. The use of the dorsal, rather than the plantar, surface of the foot at a skin temperature of 32–33°C rather than 34–35° C improves the sensitivity of the technique. Acetylcholine produces an earlier and more predictable response than normal saline, which is approximately half maximal at a current of 0.2 mA and maximal at 1.0 mA. The use of different current strengths should allow more detailed assessment of neurogenic inflammation and the effects of drugs and disease states on C fibre function.