• Hocine Slimani, Leon Plaghki, Paola Valenti, Mads U Werner, Henrik Kehlet, and Ron Kupers.
• BRAINlab, Department of Neuroscience, Faculty of Health and Medical Sciences, Panum Institute, University of Copenhagen, Copenhagen, Denmark.
• Pain. 2018 Nov 1; 159 (11): 2331-2338.

AbstractIt remains unclear which nerve fibers are responsible for mediating hyperalgesia after skin injury. Here, we examined the role of Aδ and C fibers in inflammatory hyperalgesia after a first-degree burn injury. A CO2 laser delivered ultrafast short constant-temperature heat pulses to the upper part of the lower leg to stimulate selectively the relatively fast-conducting thinly myelinated Aδ and the slowly conducting unmyelinated C fibers. Participants were asked to respond as fast as possible whenever they detected a thermal stimulus. Thresholds and reaction times to selective Aδ and C fiber activations were measured in the conditioned and the surrounding intact skin, at pre-injury, and 1 hour and 24 hours after injury. First-degree burn injury caused a significant decrease in Aδ fiber detection thresholds and a significant increase in the proportion of Aδ-fiber-mediated responses in the inflamed area 24 hours, but not 1 hour, after burn injury. No changes in heat perception were observed in the intact skin surrounding the injury. No group differences in C-fiber-mediated sensations were observed. Our findings indicate that quickly adapting Aδ fibers but not quickly adapting C fibers are sensitized when activated by short and ultrafast heat stimuli after skin burn injury. Our results further show that this change occurs between 1 hour and 24 hours after injury and that it does not extend to the skin surrounding the injury.

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