Evaluation of collateral sprouting after end-to-side nerve coaptation using a fluorescent double-labeling technique

The mechanism of end-to-side neurorrhaphy is believed to be by collateral s prouting, although evidence for this is lacking. This study validates wheth er axonal sprouting originates from the donor intact nerve by collateral sp routing with the use of a fluorescent double-labeling technique. End-to-sid e neurorrhaphy was performed on adult female Sprague-Dawley rats, Eight and 12 months postoperatively, animals were injected with true blue and diamid ino yellow into the tibialis anterior and/or gastrocnemius muscles and were transcardially perfused with fixative after 7 days of retrograde transport . The lumbar enlargement and the dorsal root ganglia from L3 to L6 were har vested and serial sectioning and fluorescent microscopy were performed. No double-labeling neurons were observed in control animals, but a group of ne urons that were greenish or yellowish in color were seen with single labeli ng. Double-labeling neurons, however, were seen in animals treated with end -to-side neurorrhaphy whether or not perineurotomy was performed. These res ults demonstrate that one parent nerve fiber can emanate another axon by co llateral sprouting following end-to-side neurorrhaphy. We hypothesize that the causes of collateral sprouting might result from "switching signals" an d/or "switching factors". (C) 1999 Wiley-Liss, Inc.