EXCITATION OF RAT CUTANEOUS NOCICEPTORS BY NOXIOUS COLD

Electrophysiological recordings were made from mechanosensitive nocice ptors innervating hairy skin of the rat hindpaw, and responses evoked by a wide range of noxious cold stimuli (20 to -12 degrees C) were det ermined. All A delta and C nociceptors sampled were excited by noxious cold, Response thresholds of A delta nociceptors were significantly h igher (colder stimulus temperatures) than thresholds of C fibers, and many exhibited response thresholds below 0 degrees C. Responses of bot h classes of nociceptors increased as stimulus temperature decreased. These data demonstrate that A delta and C nociceptors are excited by a wide range of cold stimuli and suggest that the proportion of cutaneo us nociceptors excited by noxious cold has been underestimated in prev ious studies.