Analysis of axonal regeneration through the silicone regeneration chamber: a retrograde tracing study in the rabbit facial nerve.
Transected facial nerve buccal branches in the adult rabbit were sutured to a silicone growth chamber and regeneration was observed at 3, 5, and 7 weeks postoperation. Using the retrograde axonal transport of horseradish peroxidase technique the soma in the facial motor nucleus were counted and the number was correlated with the number of axons found in the mid-cross section of the regenerating buccal branch and with the number of axons in the original nerve. The somatotopic reorganization in the facial motor nucleus was examined. The mean number of facial motoneuron soma labeled with HRP in the control was 68.0% (+/- 18.6, SE) of the axons counted at periphery. In the regenerating nerves, the labeled soma represented 2.4% of the preoperative controls after 3 weeks and rose to 8.6 and 43.9% at 5 and 7 weeks, respectively. At 3 weeks postoperative time, four of six regenerating nerves did not contain any myelinated axons at the center cross section. The ratios of labeled soma to the regenerating myelinated axons counted at the center cross section at 5- and 7-week time points were 42.2 and 61.1%, respectively. The location of the soma found in the early regeneration phase was similar to the normal distribution except in the dorsal subnucleus. After 7 weeks the proportion of labeled soma in the intermediate subnucleus declined but the general pattern replicated the distribution found in normal control preparations.