Effects of methylprednisolone on nitric oxide formation and survival of facial motor neurons after axotomy

Abstract

The aims of this study were to evaluate the effect of a high dose (160 mg/kg) of methylprednisolone sodium succinate (MPSS) on the formation of endogenous nitric oxide (NO) in the brainstem after facial nerve transection and to explore whether this effect has relevance to the survival of facial motor neurons. Guinea pig facial nerves were transected at the tympanic segment, and half were administered with MPSS, while the other half were given a vehicle of saline solution. Post operation NO formation in the brainstem at different time points was directly measured with a NO/ozone chemiluminescence technique. The surviving motor neurons were counted in histological coronal frozen sections of facial motor nuclei. The present results revealed that facial nerve transection induced a significant increase in NO formation in the brainstem by 1 week in both MPSS and saline treated groups and lasted to the end of the study (4 weeks). Compared to the saline treated group, it appeared that MPSS administration could delay the increase of nitric oxide synthase (NOS) expression and NO formation during the first 1∼2 weeks after facial nerve transection. The survival rate of facial motor neurons was significantly higher in the MPSS treated group than in the saline treated group when examined at 3 or 4 weeks after facial nerve transection. These results indicate that a high dose of MPSS elicited a delayed increase of NO formation and thus may concomitantly enhance the survival time of motor neurons after facial nerve transection.