Electrophysiological recordings were made from mechanosensitive nociceptors innervating hairy skin of the rat hindpaw, and responses evoked by a wide range of noxious cold stimuli (20 to -12°C) were determined. All Aδ and C nociceptors sampled were excited by noxious cold. Response thresholds of Aδ nociceptors were significantly higher (colder stimulus temperatures) than thresholds of C fibers, and many exhibited response thresholds below 0°C. Responses of both classes of nociceptors increased as stimulus temperature decreased. These data demonstrate that Aδ and C nociceptors are excited by a wide range of cold stimuli and suggest that the proportion of cutaneous nociceptors excited by noxious cold has been underestimated in previous studies.
- Nerve fibers