title: C-fiber structure varies with location in peripheral nerve.
abstract: Recent advances in regeneration and pain research have revealed gaps in the understanding of normal C-fiber anatomy. In the rat PNS, C-fiber axons assemble into Remak bundles, but beyond this, features of C-fiber organization are not defined. Systematic sampling and quantitation reveals that Remak bundles exiting from the L5 dorsal root ganglion (DRG) contain large numbers of axons, for example, 56% of unmyelinated axons were in bundles of >20 axons. This is different from distal nerve segments such as the hindpaw plantar nerve where the median number of axons per bundle is 3. The cross-sectional area of unmyelinated axons in dorsal root was homogeneous near the DRG but variability in axonal area increased near the spinal cord (p = 0.00001) and the mean axonal area was unchanged. Unmyelinated axons in peripheral nerve were almost always isolated from one another by Schwann cell processes; however, in dorsal root 7% to 9% of unmyelinated axons were immediately adjacent within pockets containing 2 or more axons. Remak bundles in the distal peripheral nerve clustered with other Remak bundles. We observe that multiple unmyelinated axons are juxtaposed within the C-fiber/Remak bundle and that the close association of afferent axons may have important functional implications.
authors.affiliation: Department of Neurology, Johns Hopkins School of Medicine, Baltimore, Maryland, USA. BethMurinson@hotmail.com
authors.forename: Beth Brianna
authors.initials: BB
authors.lastname: Murinson
authors.forename: John Wesley
authors.initials: JW
authors.lastname: Griffin
mesh_terms: D000818:Animals; D005727:Ganglia, Spinal / Q000502:physiology / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology / Q000648:ultrastructure*; D009431:Neural Conduction / Q000502:physiology; D009619:Nociceptors / Q000502:physiology / Q000648:ultrastructure*; D010146:Pain / Q000503:physiopathology; D010525:Peripheral Nerves / Q000502:physiology / Q000648:ultrastructure*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012583:Schwann Cells / Q000502:physiology / Q000648:ultrastructure; D012584:Sciatic Nerve / Q000502:physiology / Q000648:ultrastructure; D013126:Spinal Nerve Roots / Q000502:physiology / Q000648:ultrastructure