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Abstract
A dictum long-held has stated that the adult mammalian brain and spinal cord are not capable of regeneration after injury. Recent discoveries have, however, challenged this dogma. In particular, a more complete understanding of developmental neurobiology has provided an insight into possible ways in which neuronal regeneration in the central nervous system may be encouraged. Knowledge of the role of neurotrophic factors has provided one set of strategies which may be useful in enhancing CNS regeneration. These factors can now even be delivered to injury sites by transplantation of genetically modified cells. Another strategy showing great promise is the discovery and isolation of neural stem cells from adult CNS tissue. It may become possible to grow such cells in the laboratory and use these to replace injured or dead neurons. The biological and cellular basis of neural injury is of special importance to neurosurgery, particularly as therapeutic options to treat a variety of CNS diseases becomes greater.Stem cells can divide to self-renew and generate more committed progenies that give rise to specific tissues within the body. Pluripotent populations derived from the inner cell mass of blastocysts —embryonic stem (ES) cells — are capable of prolonged in vitro propagation while retaining the ability to generate all somatic lineages, including nervous tissue. More restricted stem cells can also be isolated from various organs at different stages of development, even in the adult. This is the case for the nervous system, where neural stem cells have been identified and expanded from both the developing and the adult brain, and might constitute suitable candidates for cell transplantation. In recent years, high profile and provocative publications have made extraordinary claims of stem cell plasticity at both nuclear and cellular levels. These include the ability of a stem cell to ‘dedifferentiate’ to a more primitive state and to ‘transdifferentiate’ from tissues such as bone marrow or tooth pulp into neurons, as well as the capacity to home exclusively to sites of injury and undergo targeted repair in disease models. There are two possible mechanisms of stem cell-induced host recovery: direct replacement of lost neurons and glia, or protection and regeneration of the host nervous system. Intriguingly, in some cases where robust functional improvements were observed in animal models of neurological diseases, a significant lack of donor cell differentiation and integration has been reported by several independent groups. This has shed new light on how stem cells might mediate brain repair.