Coding of mechanical pain by myelinated and unmyelinated nociceptors in human hairy skin

Bouchatta, O ORCID: 0000-0002-1639-0600, Thorell, O, Marshall, AG ORCID: 0000-0001-8273-7089, Rezaei, M, Barakat, A, McIntyre, S, Gerling, GJ, Mahns, DA, Olausson, H and Nagi, SS (2026) Coding of mechanical pain by myelinated and unmyelinated nociceptors in human hairy skin Pain Reports, 11 (2). e1398-. ISSN 2471-2531, 2471-2531

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Abstract

Abstract – Introduction: – In humans, cutaneous Aβ afferents are traditionally linked to discriminative touch, while pain is attributed to Aδ and C fibers. However, we previously identified thickly myelinated high-threshold mechanoreceptors (Aβ-HTMRs) that encode noxious skin indentations and evoke painful percepts when selectively activated. These afferents also display finely grained receptive fields and resilience to fatigue during sustained stimulation.Objectives: – To characterize the tuning properties of A-HTMRs under controlled mechanical stimulation and compare them with C-HTMRs.Methods: – We used a robotic stimulation system capable of delivering precise skin indentations across a wide force range (20–1000 mN). Single-unit axonal recordings (microneurography) were obtained from cutaneous afferents of the radial nerve in awake healthy participants. Both low- and high-threshold mechanoreceptors were recorded.Results: – Among 39 recorded mechanoreceptive afferents, HTMRs were distinguished by high mechanical thresholds and lack of response to soft brushing, with conduction velocities in the Aβ- and C-fiber ranges. Both A- and C-HTMRs exhibited force-dependent increases in spike count and firing rate, with A-HTMRs showing significantly stronger responses. Principal component analysis revealed distinct separation between A- and C-HTMRs, driven by A-HTMRs' robust high-force responses. Psychophysical testing indicated painful stimuli were often described as “sharp, ” and selective intraneural microstimulation of a single A-HTMR evoked localized “sharp-stinging” pain projected to its receptive field.Conclusion: – Robot-controlled stimulation confirmed both A- and C-HTMRs' role in encoding painful mechanical stimuli. The fast conduction, high firing rates, fine receptive fields, and fatigue resilience of A-HTMRs suggest a specialized nociceptive system capable of conveying rich spatial-temporal information, potentially contributing to protective behaviors.

Item Type:	Article
Uncontrolled Keywords:	A fiber, Mechanoreceptor, Microneurography, Neural coding, Nociceptor, Pain
Divisions:	Faculty of Health & Life Sciences Faculty of Health & Life Sciences > Inst. Life Courses & Medical Sciences Faculty of Health & Life Sciences > Inst. Life Courses & Medical Sciences > Inst. Life Courses & Medical Sciences (T&R staff) Faculty of Health & Life Sciences > Inst. Life Courses & Medical Sciences > Musculoskeletal & Ageing Science
Depositing User:	Symplectic Admin
Date Deposited:	03 Feb 2026 15:07
Last Modified:	23 May 2026 10:57
DOI:	10.1097/PR9.0000000000001398
Open Access URL:	https://journals.lww.com/painrpts/fulltext/2026/04...
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3196854
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