Cell damage and tissue repair in the central nervous system : Electron microscopy study of neuronal death and cell replacement

摘要

The central nervous system is vulnerable to various insults andparticularly to ischemia. To mimic ischemia, a photochemical orcompression lesion was induced in the right sensory motor cortex of ratbrains. We studied the time course of ultrastructural changes in corticalneurones after lesioning, and the occurrence of different types ofneuronal death was examined with respect to a potential therapeuticwindow. The lesion's appearance was documented by magnetic resonanceimaging (MRI). At 0.5, 1, 3, 6, 12, 24, 48 and 72 hours post-lesion,cortical neurones were examined by electron microscopy (EM). Following aphotochemical lesion, the neuropil in the lesioned area appeareddisorganised at 0.5 h, while necrotic and apoptotic cells were identifiedas separate bodies. Three hours later the tissue was disintegrated. Onthe contralateral side, ruptured membranes were found at 3 h, which is asign of irreversible cell death. Following a compression lesion,apoptotic cell death was most frequent at 12 h in the lesioned area, andsigns of secondary delayed cell death, e.g. an enlarged endoplasmaticreticulum, were found at 3 h.Following a cortical photochemical lesion, neurogenesis was studied afterbeam-walking and fluoxetine pre-treatment. Dividing cells, confirmed bybromodeoxyuridine staining and EM, migrated to the border of the lesion,and their number was enhanced after fluoxetine treatment.Embryonic stem cells and bone marrow stromal cells, labelled with theiron-oxide nanoparticle Endorem®, were implanted into rat brainsfollowing a cortical photochemical lesion or a spinal cord compressionlesion. Iron-containing cells, confirmed by Prussian blue staining andEM, were injected either into the contralateral hemisphere orintravenously into the femoral vein. The fate of labelled cells wastracked in vivo using MRI, which at seven and 14 days post-injectionshowed labelled cells migrating to the injury site.The time course of ultrastructural changes in spinal cord neuronesfollowing a compression lesion was studied. EM showed at 0.5-6 hapoptotic and at 12-72 h necrotic cell death in the vicinity of thelesion.The studies demonstrate that the chosen models are useful when studyingultrastructural changes in injured cells. As the morphology drasticallychanged at 3 h, the cellular alterations at this time point mightrepresent a breakpoint at which cells either progress towards cell deathor recover. Fluoxetine enhances stem cell migration towards a lesion.Endorem®-labelled stem cells remain viable and migrate to a lesion site;thus, Endorem® can be used for MRI tracking of implanted stem cells inanimals and humans.