Activation of NG2-positive oligodendrocyte progenitor cells during post-ischemic reperfusion in the rat brain

This study examines the alteration of oligodendrocyte progenitor cells whic h express membrane NG2 chondroitin sulfate proteoglycan after focal ischemi a 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 u p to 2 weeks. The distribution and morphological changes in NG2-positive ol igodendrocyte progenitor cells were immunohistochemically examined. Stellat e-shaped NG2-positive cells with multiple branched processes were detected in both the gray and white matter of normal brain. After 2 weeks of reperfu sion, NG2-positive cells in the area surrounding the infarction site (peri- infarct area) clearly showed enlarged cell bodies with hypertrophied proces ses. These stained strongly for NG2. Although the number of NG2-positive ce lls was increased significantly in the peri-infarct area. it decreased mark edly in the infarct core compared to controls. Double immunostaining reveal ed that these NG2-positive cells were neither astrocytes nor microglia, but NG2-positive oligodendrocyte progenitor cells. These progenitor cells are known to differentiate into oligodendrocytes. As such, this upregulation of NG2 expression may be an adaptive mechanism attempting to remyelinate rat brain tissue after ischemic insult. Only further study will elucidate this hypothesis. NeuroReport 12:2169-2174 (C) 2001 Lippincott Williams & Wilkins .