Cell proliferation and cytoarchitectural remodeling during spinal cord reconnection in the fresh-water turtle <Emphasis Type="Italic">Trachemys dorbignyi</Emphasis> |
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Authors: | María Inés Rehermann Federico Fernando Santiñaque Beatriz López-Carro Raúl E Russo Omar Trujillo-Cenóz |
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Institution: | 1.Departamento de Neurofisiología Celular y Molecular,Montevideo,Uruguay;2.Servicio de Clasificación Celular y Citometría de Flujo, Instituto de Investigaciones Biológicas Clemente Estable (IIBCE),Montevideo,Uruguay |
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Abstract: | In fresh-water turtles, the bridge connecting the proximal and caudal stumps of transected spinal cords consists of regenerating
axons running through a glial cellular matrix. To understand the process leading to the generation of the scaffold bridging
the lesion, we analyzed the mitotic activity triggered by spinal injury in animals maintained alive for 20–30 days after spinal
cord transection. Flow cytometry and bromodeoxyuridine (BrdU)-labeling experiments revealed a significant increment of cycling
cells around the lesion epicenter. BrdU-tagged cells maintained a close association with regenerating axons. Most dividing
cells expressed the brain lipid-binding protein (BLBP). Cells with BrdU-positive nuclei expressed glial fibrillary acidic
protein. As spinal cord regeneration involves dynamic cell rearrangements, we explored the ultra-structure of the bridge and
found cells with the aspect of immature oligodendrocytes forming an embryonic-like microenvironment. These cells supported
and ensheathed regenerating axons that were recognized by immunocytological and electron-microscopical procedures. Since functional
recovery depends on proper impulse transmission, we examined the anatomical axon-glia relationships near the lesion epicenter.
Computer-assisted three-dimensional models revealed helical axon-glial junctions in which the intercellular space appeared
to be reduced (5–7 nm). Serial-sectioning analysis revealed that fibril-containing processes provided myelinating axon sheaths.
Thus, disruption of the ependymal layer elicits mitotic activity predominantly in radial glia expressing BLBP on the lateral
aspects of the ependyma. These cycling cells seem to migrate and contribute to the bridge providing the main support and sheaths
for regenerating axons. |
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