title: Thermoreceptive innervation of human glabrous and hairy skin: a contact heat evoked potential analysis.
abstract: 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.
authors.affiliation: Department of Neurology, University of Michigan, 2215 Fuller Road, Ann Arbor, MI 48105, USA Neurology Research Laboratories, Veterans Affairs Medical Center, University of Michigian, 2215 Fuller Rd., Ann Arbor, MI 48105, USA Department of Neurology, Rambam Medical Center and Technion Faculty of Medicine, Haifa, Israel Department of Physiology, National Institute of Occupational Health, N-0033 Oslo, Norway Center for Experimental Medicine, Institute of Neurophysiology and Pathophysiology, University Clinic Hamburg Eppendorf Martinistr. 52, D-20246 Hamurg, Germany.
authors.forename: Yelena
authors.initials: Y
authors.lastname: Granovsky
authors.forename: Dagfinn
authors.initials: D
authors.lastname: Matre
authors.forename: Alexander
authors.initials: A
authors.lastname: Sokolik
authors.forename: Jürgen
authors.initials: J
authors.lastname: Lorenz
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Casey
mesh_terms: D000293:Adolescent; D000328:Adult; D005073:Evoked Potentials, Somatosensory; D005260:Female; D005528:Foot; D006197:Hair; D006225:Hand; D006358:Hot Temperature; D006801:Humans; D008297:Male; D009431:Neural Conduction / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D012867:Skin / Q000294:innervation*; D013823:Thermoreceptors / Q000502:physiology*; D013697:Thermosensing / Q000502:physiology