Facial nerve regeneration in the silicone chamber: the influence of nerve growth factor.

The role of nerve growth factor (NGF) was examined in the neural repair of adult rabbit facial nerves using an in vivo preparation. A 35-microliters nerve growth chamber was created by suturing the proximal and distal ends of a transected facial nerve (superior buccal branch) into a silicone tube. A gap of 8 mm in the chamber remained after removal of a 5-mm piece of nerve and insertion of the proximal and distal stumps into the tube. Animals were operated bilaterally; one side of the chamber was filled with NGF and the contralateral side was filled with Ringer's solution. Regeneration of the nerves was examined 1 to 5 weeks following the surgery. The caliber of the nerve bundle, the distribution pattern of regenerating motoneurons, axon number per fascicle, size distribution, and the total number of cells were compared to the preoperative morphology pattern found for that animal. Each buccal branch served as its own control. The NGF-filled chambers demonstrated an overall larger caliber of nerve regeneration at 5 weeks and a higher density distribution of axon growth at 3 and 5 weeks. In the early regeneration case (3 weeks), the axon growth profile exhibited more fascicles and less axons than the preoperative controls. In the more advanced state (5 weeks), the fascicle number was reduced and the axon number was increased. After 5 weeks of regeneration the number of fascicles was still more than that found in the preoperative state. Axon size at 5 weeks was 80% that of the preoperative controls and the thickness of the myelin sheath was less than the preoperative level. The histogram of the size distribution revealed the same distribution as in the preoperative control section.