Effects of neurotrophic factors on nerve regeneration monitored by in vivo imaging in thy1-YFP transgenic mice.

We evaluated sciatic nerve regeneration in thy1-YFP transgenic mice selectively expressing a fluorescent protein in their axons. Using in vivo imaging, we observed the dorsal cutaneous renervation of the hind paw for 8 weeks. Three to four weeks after the operation, the length of the regenerated nerve treated with NGF tended to be longer than that of the regenerated nerve treated with saline. Functional recovery was evaluated by a withdrawal response of the hind paw to mechanical stimuli. In NGF and GDNF groups, mice started to resume a mechanical response 4 weeks after the operation, earlier than in the saline control group. Histological and ultrastructural analyses showed that the density of unmyelinated axons in the regenerated nerve of the NGF group was larger than that of those in the saline group. These results indicate that NGF accelerated the regeneration of the sciatic nerve and thus that the monitoring of cutaneous nerve regeneration in the dorsal foot is useful to evaluate the regeneration of the sciatic nerve in vivo.