Three functionally distinct classes of C-fibre nociceptors in primates.

ABSTRACT: In primates, C-fibre polymodal nociceptors are broadly classified into two groups based on mechanosensitivity. Here we demonstrate that mechanically sensitive polymodal nociceptors that respond either quickly (QC) or slowly (SC) to a heat stimulus differ in responses to a mild burn, heat sensitization, conductive properties and chemosensitivity. Superficially applied capsaicin and intradermal injection of ?-alanine, an MrgprD agonist, excite vigorously all QCs. Only 40% of SCs respond to ?-alanine, and their response is only half that of QCs. Mechanically insensitive C-fibres (C-MIAs) are ?-alanine insensitive but vigorously respond to capsaicin and histamine with distinct discharge patterns. Calcium imaging reveals that ?-alanine and histamine activate distinct populations of capsaicin-responsive neurons in primate dorsal root ganglion. We suggest that histamine itch and capsaicin pain are peripherally encoded in C-MIAs, and that primate polymodal nociceptive afferents form three functionally distinct subpopulations with ?-alanine responsive QC fibres likely corresponding to murine MrgprD-expressing, non-peptidergic nociceptive afferents.

SUBMITTER: Wooten M 

PROVIDER: S-EPMC4072246 | biostudies-literature | 2014 Jun

REPOSITORIES: biostudies-literature