Study On The Effects And Mechanism Of X-irradiation On Peripheral Nerve Regeneration After Transverse Injury

Objective: The experiment was designed to explore the effects and mechanism of LDI on nerve regeneration and functional recovery after sciatic nerve injury in rats.Methods: Eighty two-month old Sprague-Dawley rats weighing 200g~250g were selected. After the left sciatic nerves in rats were exposed and transected, the nerves were sutured in an epineurium end-to-end anastomosis method to restore the continuity. All the rats were randomly divided into two groups:experimental group(Group A) and control group(Group B). Both groups had forty rats. Twenty-four hours after the models were built, in Group A the repaired nerves were locally irradiated by 1Gy X-ray respectively. Group B received no radiation.The observation of foot ulcers, gaits, claw reflect was performed weekly.On the third day, both group randomly selected five rats,take the left sciatic nerve and ipsilateral spinal dorsal root ganglion to measure the content of VEGF.On week two,both group randomly selected five rats,take the left sciatic nerve and ipsilateral spinal dorsal root ganglion to measure the content of GAP-43.On week four, eight and twelve post-operation, the sciatic function index of the rats was measured. Twelve weeks after surgery, the electrophysiological examination was performed to evaluate the functional recovery of the regenerated nerve. Histopathological and immunohistochemical analysis, observation of the ultrastructure with transmission electron microscope were performed to evaluate nerve regeneration and functional recovery after peripheral nerve injury functionally and morphologically.Analyzing the content of VEGF、GAP-43 to explore the mechanism of action of Ionizing radiation in promoting regeneration of peripheral nerve functional recovery.Results: 1. General observation of foot:After surgery, all the rats’ left leg and foot completely paralyzed, the plantar prolapsed, the toes were all together and flexion deformity. As the rat walk, the leg of operated side was skidding on the ground. The gaits recovery to normal in the Group A was earlier than Group B. One week to two week after surgery,the left hind foot heel of the rats in two groups all had ulcer,Group A healed earlier than Group B.After surgery,all rats did not have any limb retraction and unfold claw reflect when the left hind limb was acupunctured.Group A began to recover and return to normal earlier than Group B.2. Determination of VEGF:On the third day after surgery,content of VEGF in the left sciatic nerve of Group A is higher than Group B.3.Determination of GAP-43:Two weeks after surgery,content of GAP-43 in the left sciatic nerve of Group A is higher than Group B.4.The sciatic functional index(SFI):Two week after surgery, the rats in both groups showed the toes were flexion deformity and the plantar prolapsed, so that the value of the SFI cannot measure and calculate. From week four to week twelve, the SFI value improved. The statistics analysis showed that Group A recovered better than Group B.5.The electrophysiological examination:On twelve weeks post-operation, amplitude and conduction velocity of Group A was higher than Group B(P < 0.05).6.Histopathological and immunohistochemical analysis:On twelve weeks post-operation, the degree of the axon swelling, adhesion with surrounding tissue, structure of myelin sheaths and the expression and distribution of S-100 and NF-kb in Group A was better than Group B(P < 0.05).7.Observation of the ultrastructure with transmission electron microscope: The number and morphological structure of the nerve fiber, the diameter of the axons and the morphological structure of the myelin sheath in Group A were better than Group B.Conclusions: LDI plays a role in promoting nerve regeneration and functional recovery after peripheral nerve injury.1.LDI can promote peripheral nerve regeneration and inhibit scar formation in the early phase of peripheral nerve injury.The mechanisms include:1.LDI can increase the production of VEGF of neurons and schwann’s cells which promote the cells differentiation and growth To promote the growth of axons.2.LDI can increase the production of GAP-43,thus induce and adjust the axon regeneration and myelinization, speed up injuried nerve regeneration and repairation, promote neural functional recovery.