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Human cutaneous C fibres activated by cooling, heating and menthol
M Campero1, T K Baumann, H Bostock
1Facultad de Medicina, Clinica Alemana-Universidad del Desarrollo, Santiago, Chile. mcampero@med.uchile.cl
The Journal of Physiology
|October 14, 2009
Summary
Researchers identified specific C fibres (Type 2) activated by cooling and menthol. These fibres contribute to the perception of cold as burning, explaining puzzling sensory phenomena and neuropathic pain.
Area of Science:
- Neuroscience
- Sensory Physiology
- Dermatology
Background:
- Differential A-fibre block alters innocuous cooling sensation from cold to hot/burning.
- This change is linked to unidentified unmyelinated fibres masking or inhibited by Adelta cold fibres.
- Menthol (TRPM8 agonist) evokes burning/stinging and cold sensations, enhanced by A-fibre block.
Purpose of the Study:
- To identify C fibres in human skin activated by cooling and menthol using microneurography.
- To investigate the role of these C fibres in sensory phenomena like 'burning' cold.
- To classify C fibres based on responses to thermal stimuli and menthol.
Main Methods:
- Microneurography was used to record from human skin afferent C fibres.
- C fibres were classified as Type 1A, 1B, or 2 based on activity-dependent slowing.
- Fibre responses to heating/cooling ramps and menthol application (2-50%) were measured.
Main Results:
- Type 2 cold-sensitive C fibres were the only fibres activated by menthol.
- These fibres discharged vigorously with innocuous cooling and were sensitized by menthol.
- Type 2 fibres responded to temperatures down to 0°C and were activated by heating (13/15), indicating bimodal thermoreception.
Conclusions:
- Type 2 C fibres, activated by cooling and menthol, contribute to 'hot-burning' sensations from cold stimuli.
- Their bimodal thermoreceptive properties may explain phenomena like innocuous cold nociception and paradoxical heat.
- These findings offer insights into neuropathic pain mechanisms.
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