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S.R. Shareef, R. Stahl, S.C. Sharma, D.J. Carey; In Vivo Cha . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5212.
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Purpose: To assess the ability of rat embryonic spinal cord stem cells (SC) to survive, migrate and differentiate in mechanically damaged adult rat retinas following partial optic nerve cut. Methods: SC were isolated from 13-day fetal rat spinal cord and cultured up to one year in a defined serum free medium containing bFGF and EGF. One eye of adult Wistar rats (n=16) received partial optic nerve (ON) cut >2mm posterior to globe. At 3, 7, and 18 days post-ON cut, corresponding to peak macrophage activity, apoptosis, and 90% retinal ganglion cell (RGC) death respectively, a retinal scratch within the hemifield corresponding to the ON cut was performed and DiI labeled SC injected intravitreally at the scratch site. Similarly, the contralateral ON was exposed only; retinal scratch and SC injection were conducted at similar time points serving as control. Following 3-wk incubation, a duration optimal for SC differentiation, retinas were removed and evaluated by fluorescence microscopy. Results: Following injection of DiI (+) SC into the vitreous, labeled cells were identified in all injured retinas with signs of differentiation at all time points. In ON cut eyes, there were signs of morphological differentiation with eccentric nuclei, apical/basal processes, and growth cones with orientation towards optic nerve. DiI (+) spindle like cells were identified. Phagocytic activity was noted with clusters of round cells surrounding a core of DiI (+) SC at 3 and 7 days post-ON cut. Conclusions: SC were found to survive and differentiate in retinal hemifield corresponding to ON cut displaying charactersitics of growing neurons. Spindle-like cells may represent microglial differentiation. Cells engulfing DiI (+) SC in both eyes at only days 3 and 7 may represent blood borne marcophages responding to acute retinal injury and not to post-ON cut per se. Signals from dying or dead RGC do not appear to be inhibitory for SC survival or differentiation post-ON cut.
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