Effects Of Brain Injury With Different Location On Rat Sciatic Nerve Regeneration

Peripheral nerve injury(PNI)is one of clinically common traumas,and has a serious effect on the quality of life of patients.There will be about one million new cases around the globe.At present,suture is the main method for repairing peripheral nerve injury,but it has many inherent defects,such as foreign body reaction,second injury,and high level of dependence on advanced technology and experience.Some experts even pointed out that the functional recovery of injuried peripheral nerve had reached a plateau which was based on the technology of suture.Therefore,it is becoming the common goal for basic and clinical researches to improve the rate and extent of functional recovery of peripheral nerve,such as machenism of nerve regeneration,technologies and methods of nonsuture connection,neurotrophins and gene therapy.Traumatic brain injury(TBI)is also one of the common serious traumas,and results in many worse outcomes than peripheral nerve injury.Therefore TBI has been research focus in basic and clinical area.At the same time,many studies have shown that traumatic brain injury will increase the content of neurotrophic substances.Integrating the both results of peripheral nerve regeneration researches and brain injury studies,and inspired by the phenomenon of TBI promoting fracture healing,our project group had designed the rat model that sciatic nerve injury combined with brain injury,and finded out that a certain degree of brain injury can promote regeneration of injuried sciatic nerve.Objective:Observe whether there is differences in regeneration of the fixed side sciatic nerve injury with different side hemisphere injury,and predict the possible mechanisms of TBI promoting peripheral nerve regeneration.Methods:Ninety-nine healthy male Sprague-Dawley rats were randomly divided into equivalent three groups: Group A,right sciatic nerve transection merely;Group B,right sciatic nerve transection combined with right brain injury;Group C,right sciatic nerve transection combined with left brain injury.All of transected nerves were sutured under microscope.Classical Feeney method was used to establish a model of traumatic brain injury.After modeling,the sciatic functional index(SFI)was calculated by measuring footprints at 4th,6th,8th,10 th and 12 th week.Harvest the bilateral gastrocnemius,weigh their wet weight and calculate the wet weight ratio at 4th,8th and 12 th week.And then prepare the frozen section of experimental gastrocnemius,carry out the motor endplate acetylcholinesterase(AChE)staining and analyze the average absorption density using the software of Image-Pro Plus 6.0.Prepare the paraffin-embedded specimen of sciatic nerve,carry out the toluidine blue staining(TBS)and observe the morphologic variation through light microscope.Three rats were selected randomly from each group at 4th,8th and 12 th week.Expose the right sciatic nerve under anesthesia,inject FG solution at the distal point of 5mm from the anastomotic level.After a week,harvest spinal cords that were traced by FG and locate segments by following the sciatic nerve,prepare the frozen section of spinal cord,and then detect and calculate the number of spinal cord anterior horn motor neurons which were traced by fluoro-gold(FG)using fluorescence microscope.Results: 1.Sciatic functional index(SFI)The SFI value in each group was gradually improved with time.The SFI value was significantly higher in Groups B and C than Group A at 4 and 6 weeks after modeling(P < 0.05),and was further improved in Groups B compared with Group A and C at 8th week(P < 0.05).2.Wet weight ratio of gastrocnemiusThere is no significant difference of the rats wet weight ratio of gastrocnemius among three groups at 4th week after modeling(P > 0.05),and the wet weight ratio in Group B is significantly higher than the ratio in Group A and C at 8th week(P < 0.05).3.Acetylcholinesterase(AChE)stainingThere is no significant difference of the average absorption density of the motor endplate acetylcholinesterase(AChE)staining of gastrocnemius among three groups at 4th week after modeling(P > 0.05);and the absorbance value in Group B is significantly higher than the value in Group A and C at the 8th and 12 th week(P < 0.05).4.Fluoro-gold(FG)tracerThere is no significant difference of the number of spinal cord anterior horn motor neurons which were traced by FG among three groups at 4th week after modeling(P > 0.05);and the number of positive neurons of FG was significantly higher in Group B than the number in Group A and C at 8th and 12 th week(P < 0.05).5.Toluidine blue staining(TBS)of sciatic nerveGeneral observation: all nerves healed well and there were no obvious scar hyperplasia,no obvious adhesion to surrounding tissues and no local compression performance.Under the microscopic,at 4th week among three groups all of sciatic nerve fibers were loose,myelin sheaths were thin and axons were slender and located in the myelin sheath center.At 8th week,the sciatic nerve fibers gradually became intensive,the myelin sheaths gradually became thick,the diameter of the axons were significantly larger than before,and the result of morphological in Group B was slightly better than Group of A and C.At 12 th week,the sciatic nerve fibers became further intensive,single fibers were further enriched,the myelin sheaths gradually became more thicker than before and the thickness is uniform,and the result of morphological in Group B was more better than Group A and C.To sum up: the experimental results show that the group of the sciatic nerve transection combined with ipsilateral brain injury(Group B)are superior to the group of the sciatic nerve transection merely(Group A)and the group of the sciatic nerve transection combined with contralateral brain injury(Group C)through function and morphology assessments.Conclusions:The experiment results show that associated with ipsilateral brain damage can promote the regeneration of rat sciatic nerve injury.Combinding with the previous studies of traumatic brain injury and peripheral nerve injury,we speculate that the main elements may be that brain injury results in the production of large numbers of neurotrophic substances,forming a kind of microenvironment which can promote the peripheral nerve regeneration.The reason that there is no obvious advantage for sciatic nerve regeneration of the group of the contralateral brain injury compared to the group of the sciatic nerve transection merely may be that upper motor neurons injury decreasses the activity of lower motor neurons,then weakening the promoting effects of neurotrophic substances on the regeneration of sciatic nerve.