Development of the optic nerve of the rat - Investigative ...

734 Kuioabara Investigative Ophthalmology
October 1975
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Fig. 3. Central portion of the stalk of a 15-day-old fetus. Original neuroepithelial space (*)
is open. Cells are firmly attached to each other by apicolateral junctions (arrows). x7,000.
Insert shows details of the junctional zone. The junctions consist of chains of desmosomes and
gap junctions, The cytoplasm contains abundant polysonies. xl7,000.
the fissure. A cross-section of the fissure
zone of the optic stalk reveals a structure
similar to that of the optic cup—a single
outer cell layer and an invaginated layer
a few cells thick.
The cells of the outer layer remain unchanged
for a few days, whereas a great
number of the neuroepithelial cells of the
indented portion of the fissure, especially
of the thick layer directly next to the
retina, become degenerative and disappear
from the area during the first two
to three days following the stalk formation
(Fig. 2). The cells which have escaped
the degeneration form a tube-like
tissue of a single cell layer. These cells
are firmly attached to each other at the
apicolateral zone (Figs. 3 and 17). On
the fourteenth day, cells of the optic stalk
begin to elongate. Both the apical and the
basal attachments of the elongating cells
appear to remain intact and form large
intercellular spaces at the basal portions.
The original neuroepithelial lumen becomes
almost nonexistent on the fourteenth
day. Proliferation of the stalk cells
with mitotic activity is observed at the
apical zone until the sixteenth day. The
proliferated cells which have no basal attachment
form a large cluster at the
retrobulbar area (Figs. 4 and 5). The
cluster of cells tapers toward the posterior
but again, a large cluster appears near the
chiasm. On the fifteenth day, the stalk becomes
an oval piece having a cluster of
cells in the upper, off-center zone (Fig. 4).