This study examines the alteration of oligodendrocyte progenitor cells (OPCs), mature oligodendrocytes (OLGs) and myelination after focal ischemia in the rat brain. Adult male Sprague-Dawley rats were subjected to 90-min occlusion of the middle cerebral artery, followed by reperfusion time of up to 2 weeks. The infarct core showed a rapid and progressive decrease in the number of OPCs, OLGs, as well as the myelin density after 48 h of recirculation. The peri-infarct area exhibited a moderate reduction in the number of OLGs and the myelin density with a slight increase in the number of OPCs at 48 h of recirculation. Subsequently, a steady increase in the number of OPCs and a gradual recovery of the number of OLGs were noted in the peri-infarct area, which were accompanied by a gradual restoration of the myelin density, resulting in almost complete recovery of myelin density at 2 weeks of recirculation. OPCs in the peri-infarct area showed characteristic morphological changes such as mitotic figures, monopolar or bipolar shapes, and hypertrophied cell bodies and processes, all indicating active cell proliferation and migration. These findings suggest that the upregulation of OPCs may contribute to replenishment of OLGs and resultant remyelination in the peri-infarct area after ischemic insult.
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