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A
Posterior retina
D
A
P
V
A
P
D
A
Central retina
P
A
P
V
D
Anterior retina
P
A
V
500
m m
B
Anterior
retina
Central
retina
Posterior
retina
35
30
25
20
15
10
5
0
0
2
4
6
8
10
Tectal position (mm)
FIGURE 6.16 RGC axons overshoot their correct termination zone in a position-dependent, differential
manner in chick embryos. A. RGC axons in tectal whole mounts labeled by a small focal DiI injection into
peripheral temporal retina ( top ), central retina ( middle ), or peripheral nasal retina ( bottom ) on E11. The injec-
tion sites are shown in drawings of the retinal whole mounts and marked by arrows . The relative position-
ing of the labeled axons and branches within the tectum is shown to the right , with drawings of the outline
of each tectum on which the labeled axons and branches are traced. Axons overshoot their topographically
correct TZ (the predicted locations of the TZs are marked with black arrowheads ), but the distribution of inter-
stitial branches along the axon shafts ( white arrowheads ) is strongly biased for the location of the future TZ
along the anterior ( A )-posterior ( P ) tectal axis. Peripheral temporal axons exhibit the greatest overshoot and
peripheral nasal axons the least. B. Distribution of interstitial branches along the axon shaft expressed in per-
centage. The A-P tectal axis was divided into 500 mm bins, and the number of branches in each bin is graphed
as the percentage of total branches for each of the three groups of injections. (After Yates et al., 2001)
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