Journal of Neuroscience, Vol 2, 714-721, Copyright © 1982 by Society for Neuroscience
The arrangement of axons according to fiber diameter in the optic tract of the cat
RW Guillery, EH Polley and F Torrealba
The topographic distribution of axons according to diameter classes in the
optic tract of the cat has been studied by light and electron microscopic
methods. The subdivision of the tract into a ventral and a dorsal sector,
with the former containing the thickest fibers of the tract, has been
confirmed. In addition, there is a ventrolateral marginal zone of the tract
which contains many of the finest axons and there are gradients of fiber
diameters definable for thick and intermediate axons. The gradients show
the thinner fibers lying rostral to the thicker fibers. The major points
demonstrable by fiber diameter measurements have been confirmed by counts
of myelin lamellae. Comparison of fiber distributions in the optic tract
with the distributions in the optic nerve on the one hand and with the
geniculate terminations on the other shows that, in the region of the optic
chiasm, retinofugal axons are sorted not only according to their crossed or
uncrossed pathway but also according to their fiber diameter class and thus
are presorted in terms of their final destinations.