Adult hippocampal neurogenesis in rodents and primates: endogenous, enhanced, and engrafted

Since the studies of Ramon y Cajal, a central postulate in neuroscience has been the view that the adult brain lacks the ability to regenerate its neurons. This dogma has been challenged in the last few decades, and mounting evidence has accumulated showing the existence of a phenomenon designated 'adult neurogenesis'. De novo generation of neurons by neural progenitor cells in the adult brain is thought to be preserved only in restricted brain areas, such as the hippocampal dentate gyrus (DG) and the subventricular zone (SVZ) of the lateral ventricle. Data in the last decade coming mostly from rodent models have clearly documented that precursor cells residing in the anterior portion of SVZ and the subgranular zone of DG are responsible for adding new neurons in the olfactory bulb and DG, respectively. This raised significant interest in the clinical potential of neural progenitor cells, and recent studies have documented that brain injury is capable of activating an endogenous program of neurogenesis resulting in neuronal replacement in various cerebral regions of rodents and primates. If the newly generated neurons in the adult brain prove to be functional, it could have a tremendous impact for cell replacement therapies. Here, we summarize current knowledge of the mechanisms affecting adult hippocampal neurogenesis in both rodents and primates, and discuss its implications in developing novel strategies for the treatment of human neurological diseases.