Nociceptive sensations evoked from ‘spots’ in the skin by mild cooling and heating

Abstract

It was recently found that nociceptive sensations (stinging, pricking, or burning) can be evoked by cooling or heating the skin to innocuous temperatures (e.g., 29°, 37°C). Here we show that this lowthreshold thermal nociception (LTN) can be traced to sensitive 'spots' in the skin equivalent to classically defined warm spots and cold spots. Because earlier work had shown that LTN is inhibited by simply touching a thermode to the skin, a spatial search procedure was devised that minimized tactile stimulation by sliding small thermodes (16 mm 2 and 1 mm 2 ) set to 28° or 36°C slowly across the lubricated skin of the forearm. The procedure uncovered three types of temperature-sensitive sites (thermal, bimodal and nociceptive) that contained one or more thermal, nociceptive or (rarely) bimodal spots. Repeated testing indicated that bimodal and nociceptive sites were less stable over time than thermal sites, and that mechanical contact differentially inhibited nociceptive sensations. Intensity ratings collected over a range of temperatures showed that LTN increased monotonically on heat-sensitive sites but not on cold-sensitive sites. These results provide psychophysical evidence that stimulation from primary afferent fibers with thresholds in the range of warm fibers and cold fibers is relayed to the pain pathway. However, the labile nature of LTN implies that these lowthreshold nociceptive inputs are subject to inhibitory controls. The implications of these findings for the roles of putative temperature receptors and nociceptors in innocuous thermoreception and thermal pain are discussed.

Pruritic and Nociceptive Sensations and Dysesthesias From a Spicule of Cowhage

“…A single nociceptive quality can dominate over others in the absence of itch. For example, burning is the dominant nociceptive sensation in response to a topical application of methyl salicylate (Green and Flammer 1989b), capsaicin (Green and Bluth 1995), and mustard oil (Handwerker et al 1991), and stinging in response to lactic acid (Green and Bluth 1995) and, under certain stimulus conditions, innocuous cold (Green and Pope 2003;Green et al 2008). On the other hand, itch can sometimes dominate over lesser sensations of pricking or burning when capsaicin is topically applied to the forearm (Green 1990;Green and Flammer 1989a).…”

“…Use of the gLMS enabled comparison of the perceived intensities of itch and nociceptive sensations on a common scale (Green and Schoen 2007;Green et al 2008). The quality to be rated was indicated on the screen alongside the scale, and subjects made their ratings by moving an indicator along the scale by means of a computer mouse.…”

The paradox of pain from tooth pulp: Low-threshold “algoneurons”?

“…Another term that might sound apt is “low-threshold nociceptors”. This term has been used in relation to pain sensation evoked by highly localized heat and cooling stimuli delivered at non-noxious temperatures [19]. But again low-threshold afferents, by definition, are not nociceptors.…”

Temperature perception on the hand during static versus dynamic contact with a surface

“…This discovery followed the observation that heating or cooling the skin of the forearm to mild temperatures (e.g., 28°, 36°C) causes some individuals to feel nociceptive sensations such as burning and stinging ( low-threshold thermal nociception , LTN) in addition to warmth and cold (Green & Pope, 2003; Green & Schoen, 2005; Green & Akirav, 2007; Green, Roman, Schoen, & Collins, 2008). LTN is optimally perceived when thermal stimulation occurs as a thermode rests statically against the skin.…”