Effects Of X-ray Irradiation In Different Dosage On Nerve Regeneration After Sciatic Nerve Injury In Rats

Background and Objective: The treatment and rehabilitation of the damagedperipheral nerve has been a thorny problem for a long time. Recently, the medicalprofession has been actively exploring therapeutic methods to promote regeneration andaccelerate function recovery of injured peripheral nerve. Clinical practice for many yearshad already confirmed that physical therapy has a wide and effective role in treatment andrehabilitation. Ionizing irradiation, as an important member of physical factor family, hasmore and more reports of its therapeutic effects. But few studies had reported the effects ofionizing irradiation on nerve regeneration and functional recovery after theperipheral nerve injury. This study was to explore the effects of X-ray irradiation indifferent dosage on nerve regeneration and functional recovery after sciatic nerve injury inrats through irradiating the animal model in different doses. Through this study, we expectto provide a new method and theory basis for peripheral nerve regeneration.Methods: Eighty two-month old Sprague-Dawley rats weighing200g~250g wereselected and randomly divided into five groups. Each groups had sixteen rats. After the leftsciatic nerves in rats were exposed and transected, the nerves were sutured in anepineurium end-to-end anastomosis method to restore the continuity. Twenty-four hoursafter the models were built, the repaired nerves were locally irradiated by five differentdoses of X-ray (0Gy、0.2Gy、1Gy、7Gy、14Gy) respectively. The observation of foot ulcers,gaits, foot sensation and unfold claw reflect was performed weekly. On week four, eightand twelve post-operation, the sciatic function index of the rats was measured. Twelveweeks after surgery, the electrophysiological examination was performed to evaluate thefunctional recovery of the regenerated nerve. Local morphology of the anastomotic sitewas observed under a microscope. Histopathological and immunohistochemical analysis, observation of the ultrastructure with transmission electron microscope were performed toevaluate the effects of X-ray irradiation in different dosage on nerve regeneration andfunctional recovery after peripheral nerve injury functionally and morphologically.Results:1. General observation of foot：(1) Foot ulcers: Between week one andweek two after surgery, the left hind foot heel of the rats in each group all had ulcer. Theulcer of the1Gy group healed earlier than other groups. The healing time of the0Gy group,0.2Gy group,7Gy group and14Gy group was same.(2) Gaits: One week after surgery, legand foot of the operated side completely paralyzed, the plantar prolapsed, the toes were alltogether and flexion deformity in each group. As the rat walk, the operated leg wasskidding on the ground. The gaits recovery to normal in the1Gy group was earlier thanother groups. The recovery time of the0Gy group,0.2Gy group,7Gy group was same, andthey were all earlier than the14Gy group.(3) Foot sensation and unfold claw reflect:Between week one and week two after surgery, rats in each group did not have any limbretraction and unfold claw reflect when the left hind limb was acupunctured.Foot sensation and unfold claw reflect of the1Gy group began to recover earlier than othergroups, and return to normal earlier than other groups. The7Gy group began to recoverand return to normal earlier than the0Gy group,0.2Gy group and14Gy group. The0Gygroup,0.2Gy group and14Gy group began to recover at the same time, but the0Gy groupand0.2Gy group recovered better than the14Gy group on week twelve post-operation.2. The sciatic functional index（SFI）：Two week after surgery, the rats in each groupshowed the toes were flexion deformity and the plantar prolapsed, so that the value of theSFI cannot measure and calculate. From week four to week twelve, the SFI value of thefive groups revealed varying degrees of improvement. The statistics analysis showed thatsignificantly better recovery was observed in the1Gy group and7Gy group compared tothe other three groups at week4,8respectively (P <0.05). No significant difference of SFIvalue was observed between the1Gy group and7Gy group (P>0.05). No significantdifference of SFI value was observed among the0Gy group,0.2Gy group and14Gy group(P>0.05). A significant increase in SFI value was observed in the0Gy group,1Gy group, 0.2Gy group and7Gy group compared to the14Gy group at12weeks (P <0.05). Nosignificant difference in SFI value was observed among0Gy group,1Gy group,0.2Gygroup and7Gy group (P>0.05).3. The electrophysiological examination：On twelve weeks post-operation, amplitudeand conduction velocity of the1Gy group and7Gy group was higher than the other threegroups (P <0.05). Amplitude and conduction velocity of the1Gy group was higher thanthe7Gy group (P <0.05). Amplitude and conduction velocity of the0Gy group and0.2Gywas higher than the14Gy group (P <0.05). No significant difference was observedbetween the0Gy group and0.2Gy group (P>0.05).4. Local morphology of the anastomotic site：On twelve weeks post-operation, theanastomotic site of the1Gy group was less adhesion to surrounding tissue than the othergroups (P <0.05). The anastomotic site of the7Gy group was less adhesion to surroundingtissue than the0Gy group,0.2Gy group and14Gy group (P <0.05). The0Gy group,0.2Gygroup and14Gy group had the same degree of the adhesion to surrounding tissue (P>0.05).5. Histopathological and immunohistochemical analysis: On twelve weekspost-operation, the degree of the axon swelling, adhesion with surrounding tissue, structureof myelin sheaths and the expression and distribution of S-100in1Gy groupwas better than the other groups (P <0.05). The histopathological and immunohistochemi-cal analysis results of7Gy group were better than the0Gy group,0.2Gy group and14Gygroup (P <0.05). The histopathological and immunohistochemical analysis results of the0Gy group,0.2Gy group were similar (P>0.05), and they were all better than the14Gygroup (P <0.05).6. Observation of the ultrastructure with transmission electron microscope: Thenumber and morphological structure of the nerve fiber, the diameter of the axons and themorphological structure of the myelin sheath in1Gy group were better than other groups.The number and morphological structure of the nerve fiber, the diameter of the axons andthe thickness of the myelin sheath in7Gy group were better than the0Gy group,0.2Gy group and14Gy group (P <0.05), but7Gy group and14Gy group could observe obviousisolation of myelin sheath layers and vacuolation compare with0Gy group and0.2Gygroup. The results of the observation of the ultrastructure of the0Gy group,0.2Gy groupwere similar (P>0.05), and they were all better than the14Gy group (P <0.05).Conclusions:1Gy dose X-ray irradiation plays a role in promoting nerve regenerationand functional recovery after peripheral nerve injury. Although7Gy dose could promotethe recovery of nerve conduction velocity and limb function, slight damage effect could beobserved on ultrastructure. As the irradiation dosage increased, the damage effect would bemore and more obvious. Besides, if the irradiation dosage is too low, it will haveno effect on nerve regeneration and functional recovery. However, its mechanism andlong-term effect remain unknown, and more research needs to be done.