title: A comparison of axonal numbers in dorsal roots following spinal cord hemisection in neonate and adult rats.
abstract: This study presents myelinated and unmyelinated axon counts from thoracic dorsal roots of rats whose spinal cords were hemisected at birth or at 1 year of age. Axonal numbers from a root on the unoperated side are compared to numbers from the root of the same segment on the operated side of the animal. Counts were made 3 segments cranially and 3 segments caudally from the hemisection. In animals hemisected at birth and sacrificed at 3-8 months, there is a statistically significant increase in unmyelinated axons in roots of the operated as compared to the normal side. We interpret this as sprouting of unmyelinated axons. In animals hemisected at 1 year of age, the statistically significant change was a drop in myelinated axons in roots of the operated side. We interpret this as a loss of myelinated axon cell bodies due to axon section in the dorsal funiculus. Thus axonal sprouting occurs in young rats in our paradigm and a loss of myelinated axons occurs in older animals. We emphasize that different axonal populations respond to hemisection in different ways at different times.
mesh_terms: D000367:Age Factors; D000818:Animals; D001369:Axons / Q000648:ultrastructure; D002452:Cell Count / Q000379:methods; D005727:Ganglia, Spinal / Q000473:pathology; D008854:Microscopy, Electron; D009413:Nerve Fibers, Myelinated / Q000648:ultrastructure; D009416:Nerve Regeneration; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000473:pathology*; D013126:Spinal Nerve Roots / Q000473:pathology*