Effect Of Erythropoietin On Survival Of Facial Motoneurons And Expression Of INOS After Axotomy

Facial nerve injury is a common clinical problem in man. This is in part due to its long anatomical course in the cranium and its rather superficial location after its exit from the skull. Facial nerve injury results in facial muscular atrophy, which influences people's social interaction, as well as causes a loss of facial motoneuron in facial nucleus, which is one reason making facial neurotization difficult. The precise mechanism of cell death after facial nerve axtomy is still unknown. Current studies have indicated that increased expression of inflammatory cytokines including interleukin-1β(IL-1β), tumor necrosis factor-α(TNF-α), interleukin-6 (IL-6) and intercellular adhesion molecule-1(ICAM-1), and excess NO formation may play a important role in cell death of facial motoneurons after facial nerve transaction nitric oxide(NO)is a short-lived gaseous free radical. In the CNS, NO acts as a neuromodulator and a neurotransmitter, participating in synaptogenesis, memory formation and neuroendocrine secretion. However, if under conditions of excess formation, NO is emerging as an important mediator of neurodestructive properties. When NO meets with superoxide, a more deadly nitrite, peroxynitrite, is formed, which is a potent oxidant and nitrating agent capable of attacking and modifying proteins, lipids and DNA as well as depleting antioxidant defenses, and finally making cell dead. NO is synthasized from L-arginine and oxygen catalyzed by nitric oxide synthase(NOS). On the basis of molecular mass, subcellular location, and Ca2+ dependence at least three different forms of NOS have been classified. That included the neuronal type I (nNOS), the inducible form type II (iNOS), and the endothelial type III (eNOS). iNOS expressions is induced by inflammatory cytokines(e.g.IL-1β,IL-6,TNF-α,INF-γ, and so on) and toxins, it is the only NOS obform that is activated independent of calcium.Erythropoietin (Epo) is a glycoprotein with a molecular weight of 30.400 Da that controls the production of red cells. Contemporary literature suggests that Epo has neuroprotective effect in multiple models of nervous system injury. However, The precise mechanism of Epo producing neuroprotective effect is still unknown, and none of previous studies indicated the effect of Epo on faical motoneurons after facial nerve axotomy. Some recent studies have showed that administration of EPO may reduce the expression of inflammatory cytokines in the injured rat brain, and this may be one mechanism by which Epo producing neuroprotective effect. Therefore, the property of Epo moderating inflammatory reaction may theoretically inhibit expression of iNOS in facial nucleus after axotomy, and then may inhibit over formation of NO, protecting facial motorneurons from death. The aims of this study were to evaluate the effect of a high dose (5000U/kg) of Epo on the expression of inducible nitric oxide synthase(iNOS) in the facial nuclei after facial nerve transection and to explore whether this effect has relevance to the survival of facial motoneurons. 42 Wistar rats (250-300g) of both sexes were used in this study. The right facial nerve of 40 rats were transected at the level of the stylomastoid foramen.The left side was left untreated. Then the rats were randomly divided into 2 groups:1) Epo treated group(treated with Epo at dose of 5000U/kg body weight); 2) placebo treated group(treated with saline). The other 2 rats without any operation were served as contral group. Post operation the expression of iNOS in facial nuclei were detected by iNOS immunohistochemistry at different time point(1, 2, 3 and 4 weeks). The surviving motoneurons were counted in histological coronal paraffin sections of facial nuclei. Our results revealed that in both Epo and saline treated groups, facial nerve transection induced a significant increase of iNOS expression and a great loss of facial motoneurons in the facial nuclei at survival periods of 1, 2, 3, and 4 weeks, and there was a close correlation between iNOS expression and the loss of facial motoneurons. Compared to the saline treated group, it appeared that Epo administration could prevent the increase of the iNOS expression after facial nerve transaction. The survival rate of facial motoneurons was significantly higher in the Epo treated group than in the saline treated group when examined at 2, 3 and 4 weeks after facial nerve transection.Conclusion. These results suggest that high dose of Epo can prevent the increase of iNOS expression in facial nuclei and thus may prevent the excess formation of NO, thereby enhance the survival rate of facial motor neurons after facial nerve axotomy.