Figure 3: Hair follicle-associated myelinated nociceptors belonged to a distinct transcriptomic class.

A. Human skin immunofluorescence showed colocalization of Nefh, PGP and CGRP markers in nerve endings associated with hair follicles, confirming the existence of myelinated hair-follicle nociceptors in humans. Solid grey line marks the hair follicle. B. Fluorescent in situ hybridization (FISH) in human DRG neurons showed co-expression of TRPM8^low with genetic markers delineating the hair-follicle nociceptor population. Scale bar = 50 μm. C. Quantification of FISH data (n=180 cells from 2 donors for KIT-PIEZO2-TRPM8 and 204 cells from 2 donors for KIT-CGRP-TRPM8). KITPIEZO2-TRPM8: KIT 8.3%, PIEZO2 40.6%, TRPM8^low 12.2%, TRPM8^high 3.3% of all neurons. KIT-CALCA-TRPM8: KIT 6.4%, CALCA 45.6%, TRPM8^low 10.8%, TRPM8^high 2.0% of all neurons. D–F. Cooling responsiveness of cooling+ A-fiber nociceptors is dependent on TRPM8. Recording traces showing the response of a cooling+ A-fiber nociceptor to a drop in temperature before (D) and after menthol injections (E), inducing TRPM8 desensitization. Individual and mean (±SEM) responses of cooling+ A-fiber nociceptors to a drop in temperature under ‘Baseline (Bl)’ and ‘TRPM8 desensitization (Des.)’ conditions (2 units, tested in triplicate). In one case, the ‘Recovery (Rec.)’ phase was also recorded. F. Recording trace showing the response of a cooling+ A-fiber nociceptor to high-threshold mechanical stimulation (600 mN von Frey) under ‘TRPM8 desensitization’ condition.