Addendum to: Nature https://doi.org/10.1038/44521 Published online 21 October 1999
The Editors are issuing an Expression of Concern for this article to alert readers that panels in Fig. 5a and 5b appear to contain multiple regions where the background is unexpectedly similar. Additionally, the authors have stated that the panels in question follow the same tissue explant first at time 24 h (panel 5a), when it is healthy, and then at 52 h (panel 5b), when a subset of axons have degenerated (those distal to the floor plate), and that these two panels are meant to be illustrative of the key result, which is the quantification in panel 5c. The authors have stated that given the age of the article, the original data are no longer available. The Editors advise readers to interpret the results and conclusions of this article with caution.