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Two distinct proliferation events are induced in the hippocampus by acute focal injury Ernst, Carl

Abstract

In models of global brain injury, such as stroke or epilepsy, a large increase in neurogenesis occurs in the dentate gyrus (DG) days after the damage is induced. In contrast, more focal damage in the DG produces an increase in neurogenesis within 24 hours. In order to determine if two distinct cell proliferation events can occur in the DG, focal electrolytic lesions were made and cell proliferation was examined at early (1 day) and late (5 day) time points. At the early time point, a diffuse pattern of BrdU+ cells was present ipsilateral to the lesion. When BrdU was administered at the later time point, the number of subgranular zone BrdU+ cells was significantly greater than at 24 hours. There was a four-fold increase in new neurons at the late time point while at the early time point no significant difference in neurogenesis was observed from control hemispheres. At both early and late time points, BrdU+ cells did not arise from microglia, as they rarely co-labeled with the microglia marker ED-1. These results indicate that focal injury in the dentate gyrus can activate two proliferation reactions, and that a latent period greater than 1 day is required before the injury-induced increase in new neurons is observed.

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