Mechanical sensitization, increased axonal excitability, and spontaneous activity in C-nociceptors after ultraviolet B irradiation in pig skin. Issue 7 (July 2021)

• Record Type: Journal Article
• Authors: Werland, Fiona; de Col, Roberto; Hirth, Michael; Turnquist, Brian; Schmelz, Martin; Obreja, Otilia
• Is Part Of: Pain. Volume 162:Issue 7(2021)
• Publication Date: 2021-07
• Subjects: Pain -- C-fibre -- Axon -- Discharge frequency -- Sensitization -- Nerve growth factor -- Excitability; Pain -- Periodicals; Douleur -- Périodiques; Anesthésie -- Périodiques; Pain; Electronic journals; Periodicals; Electronic journals; 616.0472
• DOI: 10.1097/j.pain.0000000000002197
• Languages: English
• ISSNs: 0304-3959

Abstract

Abstract : Abstract: Ultraviolet B (UVB) irradiation induces hyperalgesia in human and animal pain models. We investigated mechanical sensitization, increase in axonal excitability, and spontaneous activity in different C-nociceptor classes after UVB in pig skin. We focused on units with receptive fields covering both irradiated and nonirradiated skin allowing intraindividual comparisons. Thirty-five pigs were irradiated in a chessboard pattern, and extracellular single-fibre recordings were obtained 10 to 28 hours later (152 fibers). Units from the contralateral hind limb served as a control (n = 112). Irradiated and nonirradiated parts of the same innervation territory were compared in 36 neurons; low threshold C-touch fibers (n = 10) and sympathetic efferents (n = 2) were unchanged, but lower mechanical thresholds and higher discharge frequency at threshold were found in mechanosensitive nociceptors (n = 12). Half of them could be activated with nonnoxious brush stimuli in the sunburn. Four of 12 mechanoinsensitive nociceptors were found sensitized to mechanical stimulation in the irradiated part of the receptive field. Activity-dependent slowing of conduction was reduced in the irradiated and in the nonirradiated skin as compared with the control leg, whereas increased ability to follow high stimulation frequencies was restricted to the sunburn (108.5 ± 37 Hz UVB vs 6.3 ± 1 Hz control). Spontaneous activity was more frequent in the sunburn (72/152 vs 31/112). Mechanical sensitization of primary nociceptors and higher maximum after frequency are suggested to contribute to primary hyperalgesia, whereas the spontaneous activity of silent nociceptors might offer a mechanistic link contributing to ongoing pain and facilitated induction of spinal sensitization. Abstract : Supplemental Digital Content is Available in the Text.Primary hyperalgesia in a UVB burn is linked to sensitization of nociceptors responding even to nonnoxious touch to increased axonal excitability leading to higher discharge frequencies, whereas spontaneous activity particularly in silent nociceptors might underlie the development of secondary hyperalgesia.