Astrocyte response to cerebral ischemia: Ultrastructural and autoradiographic studies

Proliferative changes in post-ischemic astrocytes were evaluated by electron microscopy and autoradiography in the rat model of 4-vessel occlusion. Within 3 hours following ischemia, astrocytes in areas of ischemic neuronal necrosis progressively enlarged, and their mitochondria significantly increased in numbers and total area. Total number of astrocytes also significantly increased by 3 hours. The astrocytic proliferation was not associated with ³H-thymidine incorporation but was accompanied by a decrease in perineuronal medium-light oligodendrocytes which fell from 50% of all perineuronal glia to 6.5% between 2 and 3 hours after ischemia. Astrocytes in areas of brain with only reversible neuronal damage showed similar changes that were mild and transient. We hypothesize that the reactive changes in astrocytes and the transformation in the perineuronal glia that occurs within several hours after cerebral ischemia may be stimulated by ionic changes in the extracellular fluid or by alterations in or loss of neuronal trophic factors.