Mobilization of Neural Stem Cells in the Adult Central Nervous System

In spite of our increased knowledge of adult neurogenesis, Cajal’s dogma of no new neurons is still fundamentally correct when viewed in the context of the brain’s intrinsic repair mechanisms. In the embryo, neurogenesis operates to generate all of the basic brain structures and circuitry. At birth, all areas of the brain down-regulate neurogenesis and, in the adult, most areas have stopped producing neurons altogether with fine tuning of the neuronal morphology and synaptic connections as the only evidence for plasticity. Evidence for persistent neurogenesis within several anatomically distinct loci in the adult brain has started to question this dogma. In spite of this evidence, the paucity of large scale neuron replacement following disease or injury leaves the dogma relatively intact. Looking forward, it seems clear that successful therapeutic mobilization of neural progenitor cells will depend on the precise modulation of local signaling responsible for recruitment of endogenous stem cells, the fate choice and migration of these cells, and their integration into the preexisting circuitry of the adult brain.