Study On The Mechanism Of Facial Nerve Injury And Regeneration

Partâ… Study on functional recovery of traumatic facial paralysis in ratObjective To systematically observe the recovery process of behaviorand function during facial nerve injury and regeneration, and then supply reliableevaluation on facial motor function experimentally. Methods Rat models of facialnerve paralysis were set up by sectioning and suturing of facial nerve.Postoperatively, the behavioral change included whisker movement and blink reflexevoked by blowing air on cornea, were observed respectively. Electroneurography(ENoG) and blink reflex (BR) were examined dynamically and all data wereanalyzed by statistic soft ware. Results Postoperatively, the whisker movementceased, the fibrillation of vibrissae appeared and blink reflex was lost or sluggish. Models began to produce barely detectable whisker movement and evoke blinkreflex 1~2 months following operation gradually, which subsequently increased atintensity and frequency. Mass contraction of the periauricular muscles were observedat the same time as eye closure 2 month after operation. ENoG recorded that thelatency of compound muscle action potential (CMAP) at experimental side began toprolong at 21 day, reached climax at 1 month and was stabilized at 3~4 monthpostoperatively, but it could not get full recovery. There were significant differences of latencies between 21~63 day and other time points (P<0.05). The amplitude andintensity didn't change as evidently as the characteristic change of latency. The R1wave of BR can be observed in rat model repetitively, which disappeared at 7~14 dayand gradually recovered 1 month following operation. When recording the R1 waveat experimental side 2 month following operation, the R1 type blink reflex response(R1oris) in orbicularis oris could be observed, which indicated the facial synkinesis,one hyperkinetic post paralytic sequela happened. Then the latency of R1 and R1orisdecreased concomitantly. There were correlations between them by statistic analysis.But the significant difference of R1oris latency was only presented between 2 monthand other time points (P < 0.05). Conclusion It is concluded that the methods ofENoG and BR could be used to evaluate the recovery process of facial motorfunction, which would do help to the studies on facial nerve injury and regenerationafter being revised.Partâ…¡Study on somatotopic reorganization of facial nucleus following rat facial-facial anastomosisObjective To observe the remodeling process of reinnervation andsomatotopy of facial motor neurons at late stage following facial nerve anastomosis,and then explore its role during facial nerve injury and regeneration. Methods Themodels were set up by facial facial anastomosis in rat. The remodeling process ofsomatotopic organization and facial motor neurons reinnervation were observed at 60,90 and 120 days following operation by Nissl staining and retrograde labelingmethods. Results (1) The results showed that there were similar numbers and organization of facial motor neurons among the Nissl staining neurons of both sidesand FG (Fluoro Gold) labeled of normal side. At operational side the FG labeledmotor neurons, representing reinnervating through the suture site successfully,decreased more than that of Nissl staining with significant difference ( p<0.05). Atnormal side the numbers of motor neurons labeled in both methods were similar. Thenumbers of FG labeled motor neurons kept stable in the regenerating process. Therewere no necrosis or apoptotic appearances in Nissl staining motor neurons atoperational side, whereas motor neurons tended to distribute more centrally. (2) Bydouble fluorescent retrograde tracing technique the motor neurons innervatedtemporal branch mainly distributed in dorsal medial and dorsal lateral divisions; thatinnervated buccal branch primarily distributed in intermedial and lateral divisions,and little in dorsal lateral divisions. It could be observed that there were no statisticsignificance of the displaced single labeled motor neurons between both sides(P>0.05). There were only double labeled neurons by FG and FR (Fluoro Ruby)presented in operational side. Conclusion The present study shows that there mightbe quite a few motor neurons at normal state but with no successful reinnervation atthe late stage postoperatively. Such type dormant neurons need further studies for itsmorphological and functional remodeling. The aberrant reinnervating appears in thelate stage and might involve in the mechanism of facial nerve regeneration andpost paralysis sequleas such as synkinesis, Besides, the hypothesis of facial nucleushyperexcitability or ephaptic transmission, may exert its role in them,too. Partâ…¢Study on plasticity of the control of motor neurons excitability foll owing facial-facial anast omosisObjective To observe the remodeling process of synaptic input andneurotransmitter receptors, and also to explore its role in the motor controls of facialnucleus during nerve injury and regeneration. Methods The model was set up byfacial facial anastomosis in rat.At postoperative day 0,7,21 and 60, synaptophysin(p38), NMDA receptor subunit 2A and AMPA receptor subunit 2 (GluR2) wereobserved by immunohistochemical method and semi quantitative reversetranscription polymerase chain reaction (RT PCR) respectively. Meantime, theultrastructure of the facial motor neurons and its synaptic contacts were observedunder transmission electron microscope (TEM). Results The intensity of p38 immunoreactivity decreased, and reached the lowest level at postoperative day 7,then increased slightly till the end of observation. NMDAR2A mRNA weredown regulated significantly in facial nucleus following operation (p<0.05), whereasAMPAR2 mRNA levels did not change significantly(p>0.05). Ultrastructurally,necrosis or apoptotic features indicative of cell death were not observed in facialmotor neurons through the whole experimental period. The number of synapsesdecreased, in compatible with the decreased of P38 immunoreactivity byimmunohistochemical method. Conclusions It indicates that the loss of synapseshappens during facial nerve regeneration. It also demonstrates that the mRNAexpression of NMDAR2A and AMPAR2 is modified to suit for the new facial motortasks following peripheral injury. It is concluded that these characteristic remodelingwould be vital in facial motor control and may involved in pathophysiology ofpost paralytic sequelas. Partâ…£Study on astrocytic plasticity in facial nucleus following facial- facial anastomosisObjective To observe the glial reactions surrounding facial motorneurons following facial anastomosis in rat. Methods At day 0,7,21 and 60following facial nerve anastomosis, the recovery process of facial movement wasobserved, the immunoreactivity of Connexin 43, Connexin 32 and glial fibrillaryacidic protein (GFAP) was observed by immunohistochemical technique,and acombined fluorescent retrograde tracing and immunofluorescent histochemicalstaining method. The ultrastructure of astrocytes was observed under transmissionelectron microscope (TEM). Results Postoperatively, facial motor function couldn'treach the normal state, and the hyperkinetic syndromes such as synkinesis oftenaccompanied at late stage. Fluoro gold (FG) retrograde tracing labeled every motorneuron of facial subnucleus, which showed an evident somatotopic organization.Normally there were a considerable number of GFAP positive cells in non nucleusareas and few one inside the facial nucleus. Postoperatively the GFAPimmunoreactivity at the operational side increased more than that at normal side, butdecreased gradually at late stage. Cx43 was detected in both motor neurons andastrocytes, whereas Cx32 only observed in neurons. Their immunoreactivity elevatedmost at postoperative day 7 but then gradually returned to the level of normal side.The ultrastructure of astrocytes showed that the sheet like process of astrocytesinvested and protected the injured facial motor neurons moderately. The apoptoticand necrosis appearance were not found in astrocytes and motor neurons.Conclusions The present study shows some characteristic changes of reactiveastrocytes during facial nerve injury and regeneration. This plasticity may involve themechanism of synkinesis and modulate the control of motor excitability. Furtherstudies on the interactions between motor neurons and surrounding glial cells willhelp to elucidate the mechanism of facial nerve regeneration and post paralyticsequelas.