Cold stimulation of teeth: a comparison between the responses of cat intradental A delta and C fibres and human sensation.

Abstract

SUMMARY1. In nembutal-anaesthetized cats, the responses of intradental Ad and C fibres to rapid cooling of the crown of canine teeth were studied.2. Single-unit recordings were obtained from a total of eighty-six intradental Ad and C fibres. The mean conduction velocity of Ad fibres was 13-9 m/s (n = 43; range: 3-6-26-0 m/s), that of C fibres was 1-3 m/s (n = 43; range: 05-2-2 m/s).3. In the intact tooth none of the identified Ad or C fibres showed any ongoing activity in the absence of intentional stimulation.4. 84% of the Ad fibres (thirty-six out of forty-three) and 88% of the C fibres (thirty-eight out of forty-three) were excited by cold stimulation of the canine tooth they were innervating.5. For all cold-sensitive Ad fibres the responses to rapid lowering of the tooth temperature were rather uniform. After an initial high-frequency discharge during the most rapid change in temperature, the discharge rate fell as the rate of change of temperature became smaller, and firing stopped completely when the temperature had reached a steady level. No firing occurred as the tooth temperature returned to its initial value. 6. A good linear correlation (r = 089) was found between the initial dynamic discharge of responding Ad fibres and the maximum rate of change of temperature achieved in a particular experiment.7. The response behaviour of C fibres to rapid cooling of the tooth was also rather uniform but different from that of Ad fibres. For C fibres no initial dynamic response phase was observed. After a mean latency of 7-3 s the fibres began to discharge regularly at a low rate at a time when the change of tooth temperature was already small.8. The firing rate of the C fibres had a weak linear correlation (r = 06) with the static tooth temperature achieved. No discharge was observed as the temperature returned to its initial value.9. For eleven cold-sensitive Ad and C fibres the receptive fields were determined by mechanical stimulation of the exposed pulp tissue. For Ad fibres the receptive * Present address: Department of Physiology, University of Helsinki, Siltavuorenpenger 20 J, SF-00170 Helsinki, Finland.PHY 391 E. JYVASJARVI AND K.-D. KNIFFKI fields were located at the pulp-dentine border, those for C fibres were located much deeper in the pulp and tended to have higher mechanical thresholds.10. When a human tooth was stimulated by a similar cold stimulus as used in the animal experiments, the sensation evoked and rated by the subjects using a fiftypoint categorical division procedure was described as a sharp, shooting pain being localized strictly to the tooth tested. Sensations other than pain were not perceived.11. Comparing the pain ratings of human subjects with the response characteristics of feline intradental Ad and C fibres to cold stimulation of a tooth, it is concluded that Ad fibres with the properties found in the cat are probably responsible for the cold-evoked dental pain sensation in man.

Diversity in the Neural Circuitry of Cold Sensing Revealed by Genetic Axonal Labeling of Transient Receptor Potential Melastatin 8 Neurons

“…These results are consistent with the phenotype of TRPM8-null mice, which are deficient in many aspects of cold sensing, including innocuous cold discrimination and nocifensive responses to noxious cold (Chung and Caterina, 2007). Moreover, psychophysical and functional data have shown cool fibers and noxious cold fibers to have distinct receptive zones in peripheral tissues (DarianSmith et al, 1973;Jyvasjarvi and Kniffki, 1987;Davis, 1998). Thus, we examined various peripheral structures including teeth, palate, tongue, and skin to determine whether TRPM8 fibers innervate these tissues in a manner that suggests that they may mediate both innocuous and noxious cold signaling, hypothesizing expression in functionally distinct subtypes of neurons or neural circuits.…”

“…5a). Thus, the first and second pains evoked by cold stimulation of the tooth are attributed to coldsensitive A␦-and C-fibers, respectively (Jyvasjarvi and Kniffki, 1987). More critically, cold-sensitive A␦-and C-fibers in both cats and rats have distinct receptive fields, with superficial endings of A␦-fibers located to the dentin and C-fibers deeper in the pulp (Fig.…”

“…The most well studied for localization of receptive zones of distinct cold fiber types are the tooth dentin and pulp (Byers and Narhi, 2002). In humans, cooling the tooth evokes a first pain that is described as sharp, transient and shooting, which is then followed by a second delayed dull aching pain (Hensel, 1982;Jyvasjarvi and Kniffki, 1987). Similarly, in animal models, cold stimulation of teeth evokes activity first in A␦-fibers, which respond with high-frequency discharges that have short latencies and adapt quickly (Jyvasjarvi and Kniffki, 1987).…”

“…In humans, cooling the tooth evokes a first pain that is described as sharp, transient and shooting, which is then followed by a second delayed dull aching pain (Hensel, 1982;Jyvasjarvi and Kniffki, 1987). Similarly, in animal models, cold stimulation of teeth evokes activity first in A␦-fibers, which respond with high-frequency discharges that have short latencies and adapt quickly (Jyvasjarvi and Kniffki, 1987). C-fibers respond concurrently to the same cold stimulus with longer latencies and low frequency, nonadapting discharges (Fig.…”

“…Consistent with the broad range of functional roles of the channel, TRPM8 neurons express markers of nociceptors as well as non-nociceptors, and have axonal properties indicative of both A␦-and C-fibers. Moreover, in the tooth, TRPM8 axons terminate in at least two distinct receptive fields in which cold fibers are known to mediate temporally and perceptually distinct pain sensations (Jyvasjarvi and Kniffki, 1987). Last, the peripheral projections of these fibers asymmetrically innervate cutaneous regions known to have noxious cold fibers, as well as different domains containing innocuous cool fibers.…”