Journal of Neuroscience, Vol 6, 1635-1642, Copyright © 1986 by Society for Neuroscience
Age-related fiber order in the ferret's optic nerve and optic chiasm
C Walsh
Although the mammalian optic tract shows a grouping of fibers by age, with
newer fibers nearer the pial surface, the possible rules for fiber ordering
in the mammalian optic nerve have not been well defined. In this study,
preferential labeling of the older retinal fibers in the ferret, a close
relative of the cat, shows that the age-related fiber order in the ferret's
optic tract reflects a systematic sorting of fibers by age that occurs in
the optic nerve, and that is maintained through the optic chiasm. The older
retinofugal fibers, dispersed throughout the nerve near the retina, come to
be limited to the perimeter of the nerve as it passes through the optic
foramen, while newer fibers come to lie nearest the center of the nerve.
These newest fibers approach the ventral surface of the brain nearer the
optic chiasm. In the chiasm, as in the tract, the oldest fibers lie
furthest from the pial surface of the brain, while newer fibers lie nearer
the surface. The age-related fiber ordering in the ferret's optic nerve,
with the newest fibers initially being furthest from the surface at the
optic foramen, differs from age-related orderings seen in nonmammalian
vertebrates, where the newest fibers are always nearest the surface. The
changing patterns of fiber ordering along the ferret's optic nerve may
relate to changes in the underlying glial structure of the developing
nerve.