C-fiber structure varies with location in peripheral nerve.
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.
Murinson
Beth Brianna
BB
Department of Neurology, Johns Hopkins School of Medicine, Baltimore, Maryland, USA. BethMurinson@hotmail.com
Griffin
John Wesley
JW
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