Response of C fibre nociceptors in the anaesthetized monkey to heat stimuli: correlation with pain threshold in humans.

Abstract

1. Ramped heat stimuli were used to compare the effects of rate of temperature change on the responses of monkey nociceptors and on heat pain threshold in human subjects. Recordings were made from twenty-five cutaneous C fibre mechano-heat nociceptors (CMHs) innervating the hairy skin in the anaesthetized monkey. Heat pain thresholds were determined on the volar forearm of eight human subjects using a converging staircase technique. 2. The heat pain threshold decreased as stimulus ramp rate increased. In contrast, the CMH heat threshold, defined as the surface temperature at which the first action potential occurred, increased as stimulus ramp rate increased. Thus, the properties of the heat stimulus that dictate heat pain threshold are different from the properties of the heat stimulus that govern the initiation of a response in nociceptors. 3. Peak discharge frequency of CMHs during the heat ramp increased with stimulus ramp rate.Heat pain threshold was correlated with achievement of a minimum discharge rate in nociceptors (0 5 Hz), rather than with the threshold for action potential initiation.

A novel method for delivering ramped cooling reveals rat behaviours at innocuous and noxious temperatures: A comparative study of human psychophysics and rat behaviour

“…Furthermore, and as noted by Banik and Kabadi, 2013 [16], these withdrawal temperatures are comparable to those generated in humans (data herein and e.g. 47.5 o C, [28]). The rat heat thresholds reported here are somewhat lower than those reported using a similar method of measuring heat hyperalgesia described by Tabo and colleagues (1998).…”

Heat‐evoked vasodilatation in human hairy skin: axon reflexes due to low‐level activity of nociceptive afferents.

“…With heat ramps of different rates of rise to the same final temperature, peak discharge rates of C fibre nociceptors may vary by orders of magnitude: at a rate of rise similar to our rapidly rising heat stimuli (5 8 0C s-) the peak discharge was about 15 s-", while at a very low rate (0-1 00C s-) similar to our slowly rising stimuli peak discharges rarely exceeded 1 s-5 (Tillman et al 1995b). The observation that pain thresholds were higher for slowly rising heat stimuli than for fast temperature steps is in line with the concept of a central pain threshold, which can only be overcome by nociceptor firing frequencies above 0 4-0 5 Hz (van Hees & Gybels, 1981;Tillman et al 1995b). Thus, pain could be elicited by intraneural microstimulation of human C fibre nociceptors with frequencies of 1 Hz and above (Ochoa & Torebjbrk, 1989).…”

Non-invasive cortical modulation of experimental pain in migraine

“…The second increase possibly reflects temporal summation of pain (Tousignant-Laflamme et al , 2008), the psychophysical correlate of wind-up (Eide, 2000). A-delta fibers are probably the source to the initial rise and fall because of rapid firing before gradually wearing out and a transition to a predominantly C fiber response occurs (Tillman et al , 1995, Treede, 1995, Tousignant-Laflamme et al , 2008. Therefore, the difference in pain ratings after 30 seconds may predominantly represent differences in C fiber activity.…”