title: Characterization of the optic nerve and retinal ganglion cell layer in the dysmyelinated adult Long Evans Shaker rat: evidence for axonal sprouting.
abstract: Myelin in the central nervous system (CNS) is hypothesized to help guide the growth of developing axons by inhibiting sprouting of aberrant neurites. Previous studies using animal models lacking CNS myelin have reported that increasing capacity for sprouting axons is negatively correlated with the degree of myelination. In the present study, we investigated the optic nerves of the recently identified Long Evans Shaker (LES) rat with prolonged dysmyelination of adult axons to determine whether the lack of myelin basic protein (MBP) in adult LES rats could manifest as increases in the population of CNS axons. We observed numerous small, unmyelinated axon profiles (<0.3 microm in diameter) clustered in bundles alongside normal caliber axons in dysmyelinated LES rats but not in normal myelinated Long Evans (LE) rats. These putative axon profiles resembled sprouting axons previously described in the CNS. Moreover, the high number of small putative axon profiles could not be accounted for by any significant increases in the number of ganglion cells and displaced amacrine cells in the ganglion cell layer when compared with normal rats as evaluated by using a variety of techniques. This finding suggests that the observed clusters of putative axon profiles were not due to developmental abnormalities in the retina but to the lack of myelin in the optic nerves of LES rats. The adult LES rat, therefore, may serve as a useful model to study the role of myelin in regulating axon development or axon regeneration after CNS injury in the adult mammalian system.
authors.affiliation: Department of Pathology and Molecular Medicine, Faculty of Health Sciences, McMaster University, Hamilton, Ontario L8N 3Z5, Canada.
authors.forename: Vinay
authors.initials: V
authors.lastname: Phokeo
authors.forename: Jacek M
authors.initials: JM
authors.lastname: Kwiecien
authors.forename: Alexander K
authors.initials: AK
authors.lastname: Ball
mesh_terms: D000818:Animals; D002452:Cell Count; D002454:Cell Differentiation / Q000235:genetics*; D048429:Cell Size / Q000502:physiology; D002490:Central Nervous System / Q000002:abnormalities* / Q000473:pathology / Q000503:physiopathology; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D004195:Disease Models, Animal; D004996:Ethidium; D005260:Female; D005456:Fluorescent Dyes; D005968:Glutamate Decarboxylase / Q000378:metabolism; D020439:Growth Cones / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D004676:Myelin Basic Protein / Q000172:deficiency; D009186:Myelin Sheath / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D009421:Nervous System Malformations / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology; D009900:Optic Nerve / Q000002:abnormalities* / Q000473:pathology / Q000503:physiopathology; D051381:Rats; D020318:Rats, Long-Evans / Q000002:abnormalities* / Q000235:genetics; D012165:Retinal Ganglion Cells / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D013266:Stilbamidines; D013869:Thiolester Hydrolases / Q000378:metabolism; D043222:Ubiquitin Thiolesterase
chemical_list: C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D005456:Fluorescent Dyes; D004676:Myelin Basic Protein; D013266:Stilbamidines; D002795:Choline O-Acetyltransferase; D013869:Thiolester Hydrolases; D043222:Ubiquitin Thiolesterase; D005968:Glutamate Decarboxylase; D004996:Ethidium