Ciliary neurotrophic factor improves muscle fibre reinnervation after facial nerve crush in young rats.

In the present study we examined the effect of recombinant human ciliary neurotrophic factor (rH-CNTF) on muscle fibre reinnervation. After facial nerve crush, rats were treated systemically with either rH-CNTF (1 mg/kg per 48 h) or saline and were killed on days 10-13 after nerve crush when muscle fibre reinnervation becomes apparent. Blind counting of the number of reinnervated motor endplates and the length of the synaptophysin-positive staining was used to assess the effect of CNTF treatment on muscle fibre reinnervation in the whisker muscle. On day 10, both treatment groups showed a limited number of reinnervated motor endplates. Both the saline- and CNTF-treated rats showed a significant increase in the percentage of reinnervated motor endplates and in the length of the synaptophysin-positive staining with time. On days 10 and 11, there was no difference in muscle fibre reinnervation between the treated groups. On days 12 and 13, the CNTF-treated rats showed an increased muscle fibre reinnervation which was significant compared to the saline-treated rats. These results suggest that after facial nerve crush in young rats, CNTF enhances muscle fibre reinnervation, most probably by stimulating the intramuscular branching. There is no support for an effect of CNTF on nerve sprouting in the proximal axonal part or on axonal elongation; the CNTF effect on intramuscular branching might be mediated by the muscle fibres.