Migration of young neurons in adult avian brain.

Neurons are born in the ventricular walls of the vertebrate central nervous system. From there, the young neurons migrate to their final destinations, where differentiation occurs. Neuronal migration has been described during the ontogeny of the avian and mammalian brain. Whereas in mammals most neurogenesis occurs during early development, in the adult avian forebrain wide-spread neurogenesis continues to occur. How do neurons born in adulthood reach their final destination? We report here that small elongated cells, born in the ventricular zone adjacent to the lateral ventricle, differentiate into mature neurons 20-40 days later, after migrating over distances of up to 5 mm. Migration rates are highest (28 micron h-1) when young neurons migrate through regions which are rich in radial glia. The adult vertebrate brain offers unique opportunities for studying factors that regulate neuronal migration, pathfinding and differentiation.