Mechanisms of neuronal migration in the adult brain

Adult neurogenesis was first observed nearly 60 years ago, and it has since grown into an important neurochemistry research field. Much recent research has focused on the treatment of brain diseases through neuronal regeneration with endogenously generated neurons. In the adult brain, immature neurons called neuroblasts are continuously generated in the ventricular-subventricular zone (V-SVZ). These neuroblasts migrate rapidly through the rostral migratory stream to the olfactory bulb, where they mature and are integrated into the neuronal circuitry. After brain insult, some of the neuroblasts in the V-SVZ migrate toward the lesion to repopulate the injured tissue. This notable migratory capacity of V-SVZ-derived neuroblasts is important for efficiently regenerating neurons in remote areas of the brain. As these neurons migrate for long distances through adult brain tissue, they are supported by various guidance cues and structures that act as scaffolds. Some of these mechanisms are unique to neuroblast migration in the adult brain, and are not involved in migration in the developing brain. Here, we review the latest findings on the mechanisms of neuroblast migration in the adult brain under physiological and pathological conditions, and discuss various issues that still need to be resolved.