Fig. 6.

Refinement of the retinotectal map occurs through topographic branch extension and ectopic branch elimination. Axons were labeled by a small focal injection of DiI into peripheral temporal retina ∼1 d before fixation on E10–E13, as in Figure 1.A, Average number of branches per axon. Branch addition from E10 to E11 occurs primarily in the termination zone (TZ), whereas branch elimination from E11 to E13 occurs primarily outside of the TZ (refer to changes in branch density in Fig.2C). B, Distribution of interstitial branches according to length expressed in percentage. The anterior (A)–posterior (P) tectal axis was divided into 500 μm bins relative to the location of the topographically correct TZ, and the number of branches in each bin is graphed as the percentage of total branches of a given range of length. Analyses were done at E12 and E13, and data were pooled. Longer interstitial branches exhibit greater topographic specificity, indicating that topographically appropriate branches are preferentially extended. See Results for n values and statistical tests.