However, two recent repor ts challenge this interpretation by demonstrating that fusion is responsible for the appearance of donorder ived neurons after systemic administration of bone marrow cells. Recent findings in rodents suggest an alternative approach to cell therapy in stroke based on selfrepair. These immature neurons migrate into the damaged striatum, where they express markers of striatal medium spiny projection neurons.Thus, the new neurons seem to Aniracetam differentiate into the phenotype of most neurons destroyed by the ischemic lesion.However, because of the new neurons die during the first weeks after stroke, they only replace a small fraction of the mature striatal neurons that have died.Several factors can increase adult neurogenesis by stimulating formation andor improving survival of new neurons, including fibroblast growth factor, stem cell factor, erythropoietin, brainderived neurotrophic factor, caspase inhibitors and antiinflammatory drugs. Whether the new neurons formed after stroke are functional is unknown.Evidence for functional neuronal replacement in the ischemically damaged brain has been reported from a model of global forebrain ischemia.Whereas the new neurons seemed to form afferent and efferent connections and to reverse some functional deficits, it cannot be excluded that the functional improvement was caused by the growth factors themselves and not by regeneration of CA neurons.There is no substantial formation of new neurons in the cerebral cortex after stroke. Notably, targeted apoptotic degeneration of cortical neurons in mice, leaving tissue architecture intact, leads to formation of new cortical neurons extending axons to the thalamus.Fluorescenceactivated cell sorting A method that allows the separation of cells expressing fluorescent marker proteins or other surface proteins that can be detected using fluorescent antibodies.A laser beam excites the fluorescent tag, and the emission of light triggers the cell sorting.It occurs naturally during meiosis, but can also be used experimentally for gene targeting to modify the sequence of a gene.Allogeneic A term that denotes subjects, tissues or cells that are of the same species, but are antigenically distinct.Cells in the neurospheres can proliferate in culture while retaining the potency to differentiate into neurons and glia.However, even reestablishment of only a fraction of damaged neuronal circuitries could have important implications.This strategy requires that the largely unknown developmental mechanisms instructing stem cells to differentiate into specific cell types will work also in the brain of the affected individual.Adequate blood supply will be crucial for survival and development of the new neurons.Neurogenesis is closely associated with angiogenesis from endothelial precursors.Angiogenesis occurs in the human brain after stroke but may have to be further stimulated to increase the yield of surviving new neurons.Administration of vascular endothelial growth factor after stroke.VEGF can also guide directed migration of undifferentiated SVZ neural progenitors.Research should now aim to identify and improve efficacy of different mechanisms, which may underlie the benefit of stem cells after stroke. Magnetic resonance imaging seems ideal for noninvasive imaging at high spatial and temporal resolution of the survival, migration and differentiation of Oxytetracycline grafted cells.Behavioral recovery must be optimized in animal models.The time window after the insult when the generation of new neurons will lead to maximum restitution of neuronal circuitries and functional recovery should be determined.