J. Viehweg et Ww. Naumann, RADIAL SECRETORY GLIA CONSERVED IN THE POSTNATAL VERTEBRATE BRAIN - ASTUDY IN THE RAT, Anatomy and embryology, 194(4), 1996, pp. 355-363
Secretory glial cells in the roof of the last diencephalic prosomer, e
pendymocytes and hypendymocytes, form the subcommissural organ. The ce
lls of this complex were labelled immunocytochemically, using an antis
erum against their specific secretory products. The study aims at the
characterization of this cell type in the rat as an anatomical model s
ituation. Radially oriented secretory glial cells remain after birth b
ehind the posterior commissure in the mesencephalic aqueduct. At about
postnatal day 10, the cell bodies descend into the conventional epend
yma and at postnatal day 25 they assume a compact, rounded appearance.
The secretory product they release is involved in the formation of Re
issner's fiber. This differentiation in phenotype is not accompanied b
y a change of the intermediate filament expression. In the adult rat t
hese cells had been labelled immunopositive for cytokeratins 8 and 18
as well as vimentin but not for glial fibrillary acidic protein. DiI-m
arking from the third ventricle and from the dorsal surface of the bra
in shows that the basal processes of ependymocytes and hypendymocytes
project to the external and internal glial limiting membrane, respecti
vely, through the commissural fiber bundles. Also the subependymal loc
ated hypendymocytes have apical processes with contacts to the cerebro
spinal fluid. When this secretory cell population is studied with resp
ect to cyto-architectonical changes during ontogeny the results lead t
o a new understanding of the subcommissural cells. They are not specia
lized ependymal cells in a regionally restricted and secondary differe
ntiated ependymal area, but rather descendants of an ontogenetically a
ncient, specific type of radial glia. Characteristic features for all
subcommissural cells are that they: (1) appear very early during ontog
eny, (2) are derived from a radial oriented glial cell type, (3) carry
at least one kinocilium, (4) possess an original intermediate filamen
t pattern, (5) release a secretory product.