Fig. 3.

Elongation of an interstitial branch is preceded by the formation of a growth cone. These images illustrate transient filopodial activity (0–48 min) leading to a stable branch over 30 μm led by a growth cone (156 min). This sequence of images was selected from 72 images acquired at 3 min intervals. Time 0 corresponds to 20 hr after plating. As shown in the last frame, once the interstitial branch is advancing forward, the distal segment of the primary axon degenerates. P and D refer to proximal and distal segments of the axon, respectively.