Transient focal cerebral ischemia-induced neurogenesis in the dentate gyrus of the adult mouse

Object. Throughout the life of a mammal, new neurons are produced each day from resident progenitor cells located in the hippocampal dentate gyrus (DG). The availability of transgenic and knockout mice enables the evaluation of specific molecular mediators of this phenomenon. To facilitate such studies the authors characterized the proliferation, survival, and maturation of progenitor cells in the DG of adult mice following transient focal cerebral ischemia. Methods. Anesthesia was induced in adult C57BL/6 mice by administering halothane. The middle cerebral artery (MCA) was then occluded for 120 minutes by applying an endovascular suture. The marker used to detect the presence of proliferating cells, 5-bromodeoxyuridine (BrdU; 50 mg/kg) was administered intraperitoneally twice daily on Days 2 through 6 after the MCA occlusion. Cohorts of mice were killed on Days 7 and 21, after which their brains were sectioned and BrdU-positive cells were detected using immunohistochemical analysis. The phenotype of the BrdU-positive cells was identified by fluorescent triple labeling by using antibodies specific for neuronal and astroglial markers together with anti-BrdU antibodies. The infarction was confirmed by applying cresyl violet staining. Compared with sham-operated control animals, there was a 4.6-fold (p<0.05) increase in BrdU-positive cells in the ipsilateral DG at Day 7 postischemia. Twenty-one percent of the newly proliferated cells survived to Day 21 postischemia. At this time, the newly proliferated cells expressed the immature and mature neuron markers doublecortin and NeuN, respectively, but none expressed the astroglial marker glial fibrillary acidic protein. Conclusions. Focal ischemia induces neurogenesis in the DG of the mouse brain; this may be critical for postischemic brain repair.