Study On The Effect Of Topically Applied Glucocorticoids On Facial Nerve In Rats

Objectives:To investigate the influence of topical glucorcorticoids on facial nerve recovery following transection injury in rats.Methods:Sixty-three rats were randomly assigned to an NS control group and two topical steroid groups.The marginal branch of facial nerve was subjected to standardized transection injury and subsequent end to end repair on each animal.Dexamethasone saturated Gelfoam(two different concentrations,2mg/ml and 5mg/ml respectively) was placed at the site of injury in the topical steroid groups whereas NS saturated Gelfoam was placed at the site of injury in the control group.Daily Myelin clearance was observed at the 1,2,3,7 days post operation(dpo) using Luxol Fast Blue(LFB) staining. Osmium tetroxide staining was performed at 2,4,8 weeks post operation and axons were counted stereologically.In addition,electrophysiological study was performed to evaluate functional recovery of the nerve at 8 weeks.Results:Myelin clearance was not obvious until at 2 dpo and was progressing from 3 to 7dpo,only some myelin debris remained at 7 dpo in each group.No significant difference was observed in myelin clearance among 3 groups.Regeneration was confirmed at 3 weeks in all groups.In steroid groups,delayed remyelination was found compared to NS group.However,no statistically significant differences were found either in axonal counts or in the electrophysiological studies among three groups.Conclusions:Topical application of small dose Dexamethasone has no influences on myelin clearance,axonal counts or electrophysiological studies but it may be associated with delayed remyelination after facial nerve injury.Clinical use of topical steroids to promote peripheral nerve regeneration warrants further study.