title: Specific paucity of unmyelinated C-fibers in cutaneous peripheral nerves of the African naked-mole rat: comparative analysis using six species of Bathyergidae.
abstract: In mammalian peripheral nerves, unmyelinated C-fibers usually outnumber myelinated A-fibers. By 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 with 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, the naked mole-rat had the lowest C:A-fiber ratio (∼1.5:1 compared with ∼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 by using as a model a mouse that loses virtually all its hair as a consequence of conditional deletion of the β-catenin gene in the skin. These β-catenin loss-of function mice (β-cat LOF mice) displayed only a mild decrease in C:A-fiber ratio compared with wild-type mice (4.42 compared with 3.81). We suggest that the selective cutaneous C-fiber deficit in the cutaneous nerves of naked mole-rats is unlikely to be due primarily to lack of skin hair follicles. Possible mechanisms contributing to this unique peripheral nerve anatomy are discussed.
authors.affiliation: Department of Neuroscience, Max-Delbrück Center for Molecular Medicine, D 13125 Berlin, Germany.
authors.forename: Ewan
authors.initials: E
authors.lastname: St John Smith
authors.forename: Bettina
authors.initials: B
authors.lastname: Purfürst
authors.forename: Tamara
authors.initials: T
authors.lastname: Grigoryan
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Park
authors.forename: Nigel C
authors.initials: NC
authors.lastname: Bennett
authors.forename: Gary R
authors.initials: GR
authors.lastname: Lewin
mesh_terms: D000349:Africa; D000818:Animals; D003711:Demyelinating Diseases / Q000235:genetics; D005260:Female; D018859:Hair Follicle / Q000166:cytology / Q000294:innervation / Q000502:physiology; D008297:Male; D019577:Mole Rats / Q000033:anatomy & histology* / Q000145:classification; D036421:Nerve Fibers, Unmyelinated / Q000145:classification / Q000502:physiology*; D010543:Peroneal Nerve / Q000737:chemistry / Q000166:cytology* / Q000502:physiology; D012867:Skin / Q000166:cytology / Q000294:innervation*; D013045:Species Specificity; D013497:Sural Nerve / Q000737:chemistry / Q000166:cytology* / Q000502:physiology