Responses of single cutaneous fibers to noxious thermal pulse stimulation of cat upper hind limb.

Previous experiments have shown that cats respond to noxious thermal pulse stimulation of the upper hind limb at an average latency of 2.3 sec. To determine if C fiber afferents could mediate this response, we recorded the response latency and threshold of single fibers of cat femoral cutaneous nerve to the same stimuli used in the behavioral experiments. Of 28 C fibers tested, 10 (36%) responded to heating; 4 (17%) of 24 fibers with conduction velocities of 2.5-30 m/sec responded to heat. All fibers but one discharged within 1.0 sec of thermal pulse onset (median: 800 msec) at an average and median threshold of 46 degrees C. Thermal nociceptors with C fiber afferents could mediate the initiation of behavioral nocifensive responses to heat in the cat.