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 v isualize arbor restructuring during activity-dependent refinement. A small number of neighboring retinal ganglion cells were labeled with DiI and obse rved in the tectum of the living animal for 5-7 hours during the period of activity-dependent refinement. In contrast to earlier stages of regeneratio n, many optic arbors were surprisingly stable, showing little or no change. The observed changes were mainly retractions, and these were affected by r etinotopic position and activity. Axon branches in retinotopic positions ch anged by much smaller amounts than ectopic axons, but in fish with retinal tetrodotoxin impulse blockade, no systematic difference was observed as a f unction of tectal position. Otherwise, impulse blockade had no notable effe cts. J. Comp. Neurol. 406:548-562, 1999. (C) 1999 Wiley-Liss, Inc.