Thermoreceptive innervation of human glabrous and hairy skin: A contact heat evoked potential analysis

Department of Neurology, University of Michigan, 2215 Fuller Road, Ann Arbor, MI 48105, USA.
Pain (Impact Factor: 5.21). 07/2005; 115(3):238-47. DOI: 10.1016/j.pain.2005.02.017
Source: PubMed


The human palm has a lower heat detection threshold and a higher heat pain threshold than hairy skin. Neurophysiological studies of monkeys suggest that glabrous skin has fewer low threshold heat nociceptors (AMH type 2) than hairy skin. Accordingly, we used a temperature-controlled contact heat evoked potential (CHEP) stimulator to excite selectively heat receptors with C fibers or Adelta-innervated AMH type 2 receptors in humans. On the dorsal hand, 51 degrees C stimulation produced painful pinprick sensations and 41 degrees C stimuli evoked warmth. On the glabrous thenar, 41 degrees C stimulation produced mild warmth and 51 degrees C evoked strong but painless heat sensations. We used CHEP responses to estimate the conduction velocities (CV) of peripheral fibers mediating these sensations. On hairy skin, 41 degrees C stimuli evoked an ultra-late potential (mean, SD; N wave latency: 455 (118) ms) mediated by C fibers (CV by regression analysis: 1.28 m/s, N=15) whereas 51 degrees C stimuli evoked a late potential (N latency: 267 (33) ms) mediated by Adelta afferents (CV by within-subject analysis: 12.9 m/s, N=6). In contrast, thenar responses to 41 and 51 degrees C were mediated by C fibers (average N wave latencies 485 (100) and 433 (73) ms, respectively; CVs 0.95-1.35 m/s by regression analysis, N=15; average CV=1.7 (0.41) m/s calculated from distal glabrous and proximal hairy skin stimulation, N=6). The exploratory range of the human and monkey palm is enhanced by the abundance of low threshold, C-innervated heat receptors and the paucity of low threshold AMH type 2 heat nociceptors.

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Available from: Kenneth Casey, Oct 05, 2015
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    • "The distinct impact of chronic stress on mast cells from glabrous and hairy skin may be explained by the different pattern of innervation [44–46] regarding both the myelinated nerve fibers [47] and the unmyelinated nociceptive nerve fibers [48]. Moreover, different functional features of Aδ and C nerve fibers innervating the human glabrous and hairy skin have been previously reported [49]. Unmyelinated type C and thin myelinated type Aδ nerve fibers are rich in various neuropeptides, such as SP and CGRP, and, together with mast cells, are key players in cutaneous neurogenic inflammation [50–52]. "
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    ABSTRACT: Mast cells play a key role in modulation of stress-induced cutaneous inflammation. In this study we investigate the impact of repeated exposure to stress on mast cell degranulation, in both hairy and glabrous skin. Adult male Wistar rats were randomly divided into four groups: Stress 1 day (n = 8), Stress 10 days (n = 7), Stress 21 days (n = 6), and Control (n = 8). Rats in the stress groups were subjected to 2 h/day restraint stress. Subsequently, glabrous and hairy skin samples from animals of all groups were collected to assess mast cell degranulation by histochemistry and transmission electron microscopy. The impact of stress on mast cell degranulation was different depending on the type of skin and duration of stress exposure. Short-term stress exposure induced an amplification of mast cell degranulation in hairy skin that was maintained after prolonged exposure to stress. In glabrous skin, even though acute stress exposure had a profound stimulating effect on mast cell degranulation, it diminished progressively with long-term exposure to stress. The results of our study reinforce the view that mast cells are active players in modulating skin responses to stress and contribute to further understanding of pathophysiological mechanisms involved in stress-induced initiation or exacerbation of cutaneous inflammatory processes.
    Mediators of Inflammation 05/2014; 2014:105950. DOI:10.1155/2014/105950 · 3.24 Impact Factor
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    • "SEPs induced by noxious laser stimulation (heat) consist of a negative-positive (NP) biphasic wave in the 160–390 ms latency range (Mouraux and Plaghki, 2007), indicating Aδ-fibre activation. Ultra-late evoked potentials (approximately 750–1100 ms; Tran et al., 2001), associated with the activation of C-fibres (Granovsky et al., 2005), can be elicited by the means of non-painful warm laser stimulations. Thus, since each type of fibre conveys specific types of sensory messages (i.e., induced by specific types of stimuli), we would be able to compare the effects of age on myelinated and unmyelinated fibres by comparing young and old adults' somatosensory and pain perception and SEPs as a function of the type of stimulation. "
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    ABSTRACT: Experimental data regarding age effects on sensitivity and pain thresholds are not always consistent, with the type of stimulus being a major source of variability. This could suggest that some types of peripheral sensory fibres undergo more important modifications with age than others. We investigated whether ageing affects differently myelinated and unmyelinated fibres. Somatosensitivity and pain perception and recorded somatosensory evoked potentials (SEPs) were assessed in younger and older adults during the selective activation of either myelinated Aδ- or unmyelinated C-fibres. Somatosensitivity for information transmitted and SEPs elicited by stimulation of C-fibres did not differ between both groups. In contrast, pain perception was lower in older than in younger adults, and older adults showed longer SEP latencies and reduced peak-to-peak amplitude, during selective stimulation of Aδ-fibres. These findings suggest that myelinated Aδ-fibres are compromised by the normal ageing process, whereas unmyelinated C-fibres seem to remain unaltered or, at least, less affected.
    European journal of pain (London, England) 04/2014; 18(4). DOI:10.1002/j.1532-2149.2013.00388.x · 2.93 Impact Factor
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    • "Thermoreceptors, nociceptors, and polymodal receptors can be stimulated using peltier chips, heat lamps, and lasers. The brain responds to these various stimulus modalities by exhibiting somatosensory-evoked potentials (SEPs), contact heat-evoked potentials (CHEPs) and laser-evoked potentials (LEPs) depending on the stimulation approach used [1], [5], [6], [7]. Collectively these evoked potentials (EPs) can exhibit unique spatial and temporal waveform morphologies arising from the different receptor populations and fiber tracts activated. "
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    ABSTRACT: Peripheral somatosensory circuits are known to respond to diverse stimulus modalities. The energy modalities capable of eliciting somatosensory responses traditionally belong to mechanical, thermal, electromagnetic, and photonic domains. Ultrasound (US) applied to the periphery has also been reported to evoke diverse somatosensations. These observations however have been based primarily on subjective reports and lack neurophysiological descriptions. To investigate the effects of peripherally applied US on human somatosensory brain circuit activity we recorded evoked potentials using electroencephalography and conducted functional magnetic resonance imaging of blood oxygen level-dependent (BOLD) responses to fingertip stimulation with pulsed US. We found a pulsed US waveform designed to elicit a mild vibration sensation reliably triggered evoked potentials having distinct waveform morphologies including a large double-peaked vertex potential. Fingertip stimulation with this pulsed US waveform also led to the appearance of BOLD signals in brain regions responsible for somatosensory discrimination including the primary somatosensory cortex and parietal operculum, as well as brain regions involved in hierarchical somatosensory processing, such as the insula, anterior middle cingulate cortex, and supramarginal gyrus. By changing the energy profile of the pulsed US stimulus waveform we observed pulsed US can differentially activate somatosensory circuits and alter subjective reports that are concomitant with changes in evoked potential morphology and BOLD response patterns. Based on these observations we conclude pulsed US can functionally stimulate different somatosensory fibers and receptors, which may permit new approaches to the study and diagnosis of peripheral nerve injury, dysfunction, and disease.
    PLoS ONE 12/2012; 7(12):e51177. DOI:10.1371/journal.pone.0051177 · 3.23 Impact Factor
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