Neurofunctional recovery after GDNF gene transfer in the recurrent laryngeal nerve-injured rat

Abstract

Problem: To assess the possibility of gene therapy for recurrent laryngeal nerve (RLN) injury, we examined the neuroprotective effect after glial cell line-derived neurotrophic factor (GDNF) gene transfer into nucleus ambiguus in a rat vagal nerve avulsion model. Morphological preservation of motoneurons has previously been demonstrated (Brain Res 962: 61–67, 2003). However, functional recovery of RLN after gene therapy has not been demonstrated. In the present study, we examined neurofunctional recovery after GDNF gene transfer in a rat RLN injury model. Methods: The left RLN of Sprague-Dawley rats was crushed for 60 seconds with forceps. Immediately after the crush and confirmation of left fixed vocal fold, an adenoviral vector encoding beta-galactosidase gene (AxCALacZ) or GDNF (AxCAhGDNF) was directly injected into the crushed site of RLN. Transgene expression by AxCALacZ in nucleus ambiguus was examined by X-gal histochemistry. Measurement of conduction velocity (CV) of RLN and laryngoscopy to check motion recovery of the left vocal fold were performed 2 and 4 weeks postoperation. The cross-section of RLN was histologically examined after epon/toluidine blue staining. Results: Motoneurons and their neurites in nucleus ambiguus were labeled with X-gal staining 4 days after AxCALacZ injection, indicating successful induction of foreign gene into the nucleus ambiguus by retrogradely transported adenoviral vector from the crushed site. In comparison between AxCAhGDNF-injected, AxCALacZ-injected, and noninjected animals, significantly better CV of RLN and better vocal fold motion recovery rate were observed in AxCAhGDNF-injected animals 2 and 4 weeks postoperation. RLN cross section of AxCAhGDNF-injected animals showed better myelination compared to the controls. Conclusion: Injection of adenoviral vectors into the crushed site of RLN successfully induced the foreign gene into motoneurons in nucleus ambiguus. Adenoviral GDNF gene transfer after RLN crush improved the CV of RLN and motion recovery of the paralyzed vocal fold. Significance: Adenoviral GDNF gene therapy may provide neurofunctional recovery in humans with a paralyzed vocal fold. Support: None reported.