Specific paucity of unmyelinated C-fibers in cutaneous peripheral nerves of the African naked-mole rat: comparative analysis using six species of bathyergidae


  • E.S.J. Smith
  • B. Purfürst
  • T. Grigoryan
  • T.J. Park
  • N.C. Bennett
  • G.R. Lewin


  • Journal of Comparative Neurology


  • J Comp Neurol 520 (12): 2785-2803


  • In mammalian peripheral nerves, unmyelinated C-fibers usually outnumber myelinated A-fibers. Using transmission electron microscopy we recently showed that the saphenous nerve of the naked mole-rat (Heterocephalus glaber) has a C-fiber deficit manifested as a substantially lower C:A-fiber ratio compared to other mammals. Here we determined the uniqueness of this C-fiber deficit by performing a quantitative anatomical analysis of several peripheral nerves in five further members of the Bathyergidae mole-rat family: silvery (Heliophobius argenteocinereus), giant (Fukomys mechowii), Damaraland (Fukomys damarensis), Mashona (Fukomys darlingi) and Natal (Cryptomys hottentotus natalensis) mole-rats. In the largely cutaneous saphenous and sural nerves we found that the naked mole-rat had the lowest C:A-fiber ratio (~1.5:1 compared to ~3:1), whereas in nerves innervating both skin and muscle (common peroneal and tibial) or just muscle (lateral/medial gastrocnemius), this pattern was mostly absent. We asked whether lack of hair follicles alone accounts for the C-fiber paucity using a mouse model, which loses virtually all its hair as a consequence of conditional deletion of the beta-catenin gene in the skin. These beta-catenin loss-of function mice (beta-cat LOF mice) displayed only a mild decrease in C:A-fiber ratio compared to wild-type mice (4.42 compared to 3.81). We suggest that the selective cutaneous C-fiber deficit in the cutaneous nerves of naked mole-rats is unlikely to be primarily due to lack of skin hair follicles. Possible mechanisms contributing to this unique peripheral nerve anatomy are discussed.