Changes in growth inhibitory factor mRNA expression compared with those in c-jun mRNA expression following facial nerve transection.

We investigated growth inhibitory factor (GIF) mRNA expression within the rat facial nucleus with the aid of in situ hybridization. We found that GIF mRNA was expressed abundantly in the facial motoneurons of sham operated animals, and that this gene expression decreased after transection of the facial nerve. This decrease of GIF mRNA was first detected on the third day and was maintained for at least five weeks after transection of the nerve. Changes in c-jun, an immediate early gene, were also investigated with this model, and it was found that c-jun mRNA started to increase in the facial nucleus on the first day and that this increase was maintained for at least 5 weeks. These results suggest that the facial motoneurons, when their axons are transected, continuously respond to the injury and that GIF mRNA is actively suppressed to reduce the inhibition of neurite outgrowth in order to regenerate the axons.