Journal of Neuroscience, Vol 4, 1045-1051, Copyright © 1984 by Society for Neuroscience
Rules of order in the retinotectal fascicles of goldfish
CA Stuermer and SS Easter Jr
Individual fascicles of retinal axons were labeled in the goldfish tectum
with horseradish peroxidase (HRP). The contralateral retina was later
processed for HRP histochemistry to mark the cells that had axons in the
fascicles. Labeled cells were found in a partial half anulus in ventral
hemiretina, centered on the optic disk. The distance of the partial anulus
from the disk depended on which tectal fascicle had been labeled; the more
rostrocentral the fascicle, the smaller was the annular radius. The angular
subtense of the partial anulus with respect to the disk depended on where
(along its tectal course) the fascicle had been labeled; the more rostral
the label site, the longer was the angular subtense. These results were
interpreted in the context of retinotectal growth, and it was inferred that
the axons followed two rules: (1) grow in along the edge of the tectum and
(2) exit and terminate in order, axons from temporal retina first, nasal
retina last. These rules would produce a retinotopic projection in
peripheral tectum, but they require that some of the terminals already in
place must shift as the tectum grows.
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