Be. Reese et al., GLIAL DOMAINS AND AXONAL REORDERING IN THE CHIASMATIC REGION OF THE DEVELOPING FERRET, Journal of comparative neurology, 349(2), 1994, pp. 303-324
This study has examined the developing glial architecture of the optic
pathway and has related this to the changing organization of the cons
tituent axons. Immunocytochemistry was used to reveal the distribution
of glial profiles, and DiI was used to label either radial glial prof
iles or optic axons. Electron microscopy was used to determine the dis
tribution of glial profiles, axons, growth cones, and wrists at differ
ent locations along the pathway. Three different glial boundaries were
defined: Two of these are revealed as changes in the distribution of
vimentin-immunoreactive profiles occurring in the prechiasmatic optic
nerve and at the threshold of the optic tract, respectively, and one b
y the presence of glial fibrillary acidic protein (GFAP)-immunoreactiv
e profiles at the chiasmatic midline. The latter, midline boundary may
be related to the segregation of nasal from temporal optic axons. The
boundary at the threshold of the optic tract coincides with the segre
gation of dorsal from ventral optic axons that emerges at this locatio
n in the pathway. The segregation of old from young optic axons is sho
wn to occur only gradually along the pathway. Glial profiles are most
frequent in the deeper parts of the tract, coursing parallel to the op
tic axons and orthogonal to their usual radial axis. These are suggest
ed to arise from later-growing radial glial fibers that are diverted t
o grow amongst the older optic axons. Those glial profiles may subsequ
ently impede axonal invasion, thus creating the chronotopic reordering
by forcing the later-arriving axons to accumulate superficially. (C)
1994 Wiley-Liss, Inc.