The Effect Of Reinjury On Facial Nerve Regeneration And Its Related Mechanism

Objective:To investigate the relationship and the related mechanisms between the facial nerve regeneration and its reinjury,to analyze the capability of facial nerve regeneration at different time points after reinjury,and to sum up within what time point the reinjury can significantly promote facial nerve regeneration.Methods:Facial nerve injury and reinjury animal models(adult male Wistar rats):GroupⅠ:The right facial nerve stem(including postaurical branch) was transected approximately 3 mm distal from the stylomastoid foramen,and a 2 mm segment of the distal portion of the nerve was removed. The distal stump was ligated with 3 / 0 silk threads to prevent the regeneration of the axons from their targets,and 5 / 0 silk threads was used to label the proximal nerve stump.GroupⅡ(reinjury group,chronic axotomy plus second axotomy group):12,20,28,36,48 weeks after the initial facial nerve axotomy,the proximal lmmnerve stump(including the posterior auricular branch) was re-axotomized.GroupⅢ:(Bilateral facial nerve axotomy plus right side facial nerve re-axotomy group):12 weeks after bilateral facial nerve axotomy,both of the facial nerve stumps were exposed again,and the right side facial nerve 1 mm proximal stump was re-axotomized.The Left incision was directly sutured without nerve injury.GroupⅣ:(reinjury plus shh(Sonic Hedgehog) signaling pathway blocking group):16 weeks after the initial facial nerve axotomy, the proximal 1mm nerve stump(including the posterior auricular branch was re-axotomized,and a 1mm~3 gelfoam soaked with cyclopamine in different concentration(1.0μg/ml,5.0μg/ml,10μg/ml,dissolved in 45%(w/v) 2-hydroxypropyl-β-cyclodextrin in PBS ) or simply with 45%(w/v) 2-hydroxypropyl-β-cyclodextrin in PBS group was placed at the end of the proximal nerve stump.The distal stump was ligated with 3 / 0 silk thread.The intact contralateral sides were served as control.Methods of Immunohistochemistry,RT-PCR,Western blotting analysis of the brain stem cryosections(including bilateral facial nuclei) were used.The gene expression of GAP43,Shh,Smoothened were detected and analyzed.The number of survived motor neurons was determined and counted.With transmission electron microscope examination,the facial nerve regeneration after injury,reinjury,and reinjury plus shh signaling pathway blocking were analyzed.Results:Winthin4monthsafterthefacialnerveinitialaxotomy,the reinjury on facial nerve could induce the gene GAP43 expression upregulation in the experimental side motor neurons.At the same time, shh and its receptor smoothenedmRNA were upregulated.The GAP43 expression upregulation was apparently related to the upregulation of shhmRNA and smoothenedmRNA.The different time points after the initial facial nerve axotomy,the different effect of reinjury induced facial nerve regeneration was.If the reinjury occured 5-7 months after the initial facial nerve axotomy,the GAP43 expression of the motor neurons in ipsilateral side became similar to or slightly higher than that of the contralateral side,and weaker than that of the contralateral side 9 months after the initial facial nerve axotomy.When the Shh signaling pathway was blocked,the SmoothenedmRNA and the GAP43mRNA were downregulated simultaneously.The transmission electron microscope examination results showed that the axon regeneration of the facial nerve diminished or even disappeared after the Shh signaling pathway was blocked.Conclusions:Reinjury on the chronic axotomized facial nerve can promote its regeneration.The regeneration ability of the facial nerve was related to the time point of the second axotomy(that is reinjury). If the reinjury occured 4 months within the initial facial nerve axotomy, it can promote facial nerve regeneration markedly.On the contrary,if it occurred more than 5 months later,facial nerve regeneration ability was similar to or weaker than that of the contralateral side.The mechanism of the reinjury promote facial nerve regeneration is related with the activation of shh signaling pathway. Objective:To investigate an effective method of quantitative analysis of the facial nerve and its adjacent structures based on three-dimensional CT image reconstruction of temporal bone structures on personal computer,which can provide a series of important parameters for ear and the lateral skull base surgery.Methods:The inner structures of temporal bone from CT images of 34 healthy adults were reconstructed.The precise measurement of facial nerve and its adjacent structures were accomplished by using the Able Software 3D-DOCTOR.The complicated relationship and their morphologic characteristics were clearly presented.The precise measurement of some parameters between facial nerve and its adjacent structures could easily be processed with the software.Based on all obtained data,the relationship of facial nerve and its adjacent structures were effectively summarized and analyzed. Results:3D images of temporal bone structures,including the facial nerve, tympanic annulus,cochleariform process,cochlea,semicircular canals, jugular fossa and carotid artery,were reconstructed.The quantitative data of the facial nerve and its adjacent structures,especially the detailed spatial relationships between facial nerve and the surface of mastoid process or tympanomastoid fissure,was analyzed.Some parameters obtained from measuring the distance or angle between the facial nerve and its adjacent structures in the three-dimensional models had some extent regularity,which were benefit to design surgical approach and determine the position of facial nerve during relevant operation.Conclusion:3D reconstruction of CT images clearly displayed the detailed structures of temporal bone.The quantitative data of facial nerve and its adjacent structures are very useful for temporal bone surgery.