{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,24]],"date-time":"2026-09-24T21:38:04Z","timestamp":1790285884962,"version":"4.1.0"},"reference-count":37,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2025,3,19]],"date-time":"2025-03-19T00:00:00Z","timestamp":1742342400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Pain Res."],"abstract":"<jats:p>\u201cSilent\u201d C-nociceptors are crucial for inducing the axon reflex erythema in humans and may also contribute to spinal sensitization such as secondary hyperalgesia. Electrical slow depolarizing stimulation paradigms activate unmyelinated C-fibers [25\u2005ms half-sine (HS) profile] whereas A-fibers are stimulated by 500\u2005\u00b5s rectangular (R) pulses. We therefore expect to provoke larger areas of axon-reflex flare (silent nociceptor activation) and secondary hyperalgesia to HS stimuli. We compared axon-reflex erythema and secondary mechanical hyperalgesia areas induced by intracutaneous electrical HS and R stimuli using stimulation intensities that induced pain ratings of 3 and 6 on a numeric rating scale (NRS 0\u201310) in 24 healthy volunteers. Slowly depolarizing C-fiber stimulation was linked to lower current intensities required to induce pain (NRS 6: HS 3.6 vs. R 9.2\u2005mA, <jats:italic>p<\/jats:italic>\u2009=\u20090.001) and resulted in larger axon reflex erythema for high stimulus intensities (AUC<jats:sub>Flare<\/jats:sub>: NRS 6, 320.7 vs. 234.1\u2005cm<jats:sup>2<\/jats:sup>\u22c5min, <jats:italic>p<\/jats:italic>\u2009=\u20090.015; NRS 3, 79.1 vs. 51.0\u2005cm<jats:sup>2<\/jats:sup>\u22c5min; <jats:italic>p<\/jats:italic>\u2009=\u20090.114). Preferential C-fiber stimulation indicated a correlation of axon-reflex erythema with the areas of secondary mechanical hyperalgesia (NRS 6: <jats:italic>r<\/jats:italic>\u2009=\u20090.21, <jats:italic>p<\/jats:italic>\u2009=\u20090.036; NRS 3: <jats:italic>r<\/jats:italic>\u2009=\u20090.48, <jats:italic>p<\/jats:italic>\u2009=\u20090.0016). In contrast, the mean area of secondary mechanical hyperalgesia did not differ between HS and R [AUC<jats:sub>Hyper<\/jats:sub>: NRS 6, 1,555 (HS) vs. 1,585\u2005cm<jats:sup>2<\/jats:sup>\u22c5min (R), <jats:italic>p<\/jats:italic>\u2009=\u20090.893; NRS 3, 590 (HS) vs. 449\u2005cm<jats:sup>2<\/jats:sup>\u22c5min (R), <jats:italic>p<\/jats:italic>\u2009=\u20090.212] albeit it developed faster during HS. Our data confirm that silent nociceptors provoke the axon reflex erythema, but their role in secondary hyperalgesia appears to be less crucial.<\/jats:p><jats:p><jats:bold>Clinical trial number:<\/jats:bold> NCT0544026<\/jats:p>","DOI":"10.3389\/fpain.2025.1556429","type":"journal-article","created":{"date-parts":[[2025,3,19]],"date-time":"2025-03-19T07:08:33Z","timestamp":1742368113000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":3,"title":["Preferential C-nociceptor stimulation facilitates peripheral axon reflex flare, but not secondary mechanical hyperalgesia"],"prefix":"10.3389","volume":"6","author":[{"given":"Luana","family":"Daneffel","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Roman","family":"Rukwied","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Martin","family":"Schmelz","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wilhelm","family":"Ruppen","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tobias","family":"Schneider","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2025,3,19]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"395","DOI":"10.1097\/00000542-200108000-00022","article-title":"A new model of electrically evoked pain and hyperalgesia in human skin: the effects of intravenous 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