Figure 5.

Bath application of BayK 8644 increases differential process outgrowth. A, Time-lapse images of a cortical neuron exposed to BayK for 8 h, showing extension of the primary axon and retraction of the branch. B, C, Phase images showing the effect of BayK on increasing differential outgrowth between different processes from the same axon. B, After 12 h of exposure to BayK, the primary axon (black arrowhead) extended whereas the two branches (green and red arrowheads) completely retracted. C, After 20 h of exposure to BayK the primary axon (black arrowhead) retracted back to the nearest branch point whereas two branches (green and red arrowheads) extended. D, An example of a control neuron with only small differences in rates of outgrowth during the imaging session. In contrast to BayK treatment, differences in rates of outgrowth are smaller in control cultures. E, Quantifications of the effect of BayK on increasing differential outgrowth. E, Left, Bath application of BayK increased the number of neurons with significant differences in outgrowth rates among their axonal processes compared with control (***p < 0.001, Fisher's exact test, n ≥ 129 neurons from 5 experiments) (see Materials and Methods). Right, Bath application of BayK significantly increased the number of neurons that had both extending and retracting axonal processes (***p < 0.001, Fisher's exact test, n ≥ 129 neurons from 5 experiments). Scale bar, 20 μm.