In the brain of adult mice, cells that divide in the subventricular zo
ne of the lateral ventricle migrate up to 5 millimeters to the olfacto
ry bulb where they differentiate into neurons. These migrating cells w
ere found to move as chains through a well-defined pathway, the rostra
l migratory stream. Electron microscopic analysis of serial sections s
howed that these chains contained only closely apposed, elongated neur
oblasts connected by membrane specializations. A second cell type, whi
ch contained glial fibrillary acidic protein, ensheathed the chains of
migrating neuroblasts. Thus, during chain migration, neural precursor
s moved associated with each other and were not guided by radial glial
or axonal fibers.