Erythropoietin enhances survival of facial motor neurons by inhibiting expression of inducible nitric oxide synthase after axotomy

The aims of this study were (1) to evaluate the effect of high-dose erythropoietin (EPO; 5000 U/kg) on expression of inducible nitric oxide synthase (iNOS) in the facial nucleus after facial nerve transection; and (2) to explore whether this effect is relevant to facial motor neuron survival. Forty-two Wistar rats (250–300 g) of both sexes were used in this study. The right facial nerves of 40 rats were transected at the level of the stylomastoid foramen, with the left sides left untreated. The rats were randomly divided into 2 groups: (1) EPO group (treated with EPO twice per week at a dose of 5000 U/kg bodyweight); (2) saline group (treated with saline). The 2 rats that did not undergo axotomy served as the control group. After axotomy, expression of iNOS in the facial nucleus was detected by iNOS immunohistochemistry at various time points, and the number of surviving motor neurons was counted in coronal paraffin sections of the facial nucleus. In both the EPO and saline groups, axotomy caused a significant increase in iNOS expression in the facial nucleus at 1, 2, 3, and 4 weeks after axotomy. iNOS expression was lower in the EPO group than in the saline group. At 2, 3 and 4 weeks after axotomy, a significantly greater proportion of facial motor neurons survived in the EPO group than in the saline group. These results indicate that a high dose of EPO attenuates the increase in iNOS expression in the facial nucleus after facial nerve transection, and thus may enhance the survival of facial motor neurons.