In the central nervous system cell migration is usually restricted to
developmental periods and occurs mainly radially, following the radial
glia. Nevertheless, in the subependymal layer of the adult rodent for
ebrain tangential migration of newly generated neuronal precursors dir
ected to the olfactory bulb, which follow a well-defined pathway witho
ut dispersion, has been recently demonstrated. In the present study, b
y using light microscopic immunocytochemistry for glia-associated anti
gens (glial fibrillary acidic protein, S-100 and vimentin), and conven
tional electron microscopy, we observed a dense meshwork of astrocytic
cells and processes throughout the subependymal layer of the adult ra
t. These cells were organized to form tangentially oriented glial tube
s in the subependymal layer of the lateral ventricle and in its rostra
l extension to the olfactory bulb. Glial tubes were particularly evide
nt within the rostral extension and were widely intercommunicating. Us
ing markers for the proliferating/migrating cells of the rostral migra
tory stream (5-bromo-2'-deoxyuridine, PSA-NCAM, class III beta-tubulin
), we provide evidence that long chains of PSA-NCAM/beta-tubulin-posit
ive, newly generated cells are consistently observed inside the glial
tubes. These results demonstrate the existence of a peculiar glial org
anization within the subependymal layer of the adult rat, consisting o
f long astrocytic tubes that likely represent a new type of glial guid
ance, accounting for the tangential migration of a high number of cell
s along their restricted pathway, to the olfactory bulb. Copyright (C)
1997 Elsevier Science Inc.