Rapid Remodeling of Retinal Arbors in the Tectum with and without Blockade of Synaptic Transmission
Dynamic rearrangements of axon terminal arbors may be critical for establishing appropriate connections in the developing nervous system. Here, the changes in complex retinal axon arbors in the tecta of live Xenopus larvae were followed during the formation of the topographic retinotectal projection. Three-dimensional reconstructions of terminal arbors made with a confocal microscope at hourly intervals revealed rapid remodeling of arbor extensions. Shorter branches were extended and retracted very rapidly, suggesting that they probe the environment for the optimal sites to form stable branches. About 27% of longer branches were present throughout the entire observation period and may be sites of stabilized synaptic contacts. Treatment of the animals to block postsynaptic activity resulted in increased rates of arbor rearrangements, which may coincide with decreased synapse stability. These studies reveal the dynamic behavior of nerve arbors and provide estimates for the lifetimes of retinotectal branches.
© 1994 Cell Press. Received 24 August 1993, Revised 1 February 1994. We thank Barbara E. S. Fox for performing the electrophysiology depicted in Figure 7. We would also like to thank Frank Truong for assistance in analyzing the data and Mary Flowers for printing some of the figures. This work was supported by grants from the National Institutes of Health (EY06314) to N. A. O'R., the McKnight foundation to H. T. C., and the National Institutes of Health (MH49176 and EY08363) to S. E. F. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC Section 1734 solely to indicate this fact.