Activity-dependent refinement in the goldfish retinotectal system is mediated by the dynamic regulation of processes withdrawal: an in vivo imaging study.

Imaging of regenerating optic fibers in living adult goldfish was used to visualize arbor restructuring during activity-dependent refinement. A small number of neighboring retinal ganglion cells were labeled with DiI and observed in the tectum of the living animal for 5-7 hours during the period of activity-dependent refinement. In contrast to earlier stages of regeneration, many optic arbors were surprisingly stable, showing little or no change. The observed changes were mainly retractions, and these were affected by retinotopic position and activity. Axon branches in retinotopic positions changed by much smaller amounts than ectopic axons, but in fish with retinal tetrodotoxin impulse blockade, no systematic difference was observed as a function of tectal position. Otherwise, impulse blockade had no notable effects.