The Effect Of Methylcobalamin On Regeneration Of Motor End Plate With Injured Peripheral Nerves

The recovery of skeletal muscle functional has always been a big hot issue after peripheral nerve injury in the field of neuroscience. Skeletal muscle is a target organ of peripheral nervous system, the normal function of skeletal muscle maintenance depends on the nerve's dominance and regulation. Irreversible muscle atrophy will occur or even loss its function if the skeletal muscle can not receive promptly reinnervation after peripheral nerve injury. Somatic motor nerve terminals, in morphology, which is often call ed motor end plates (MEP) and in the physiology it is known as the neuromuscular junction(NMJ),it i s a specialized region exists between the skeletal muscle and the nerve fiber. The functional recovery of motor nerves depends on the regeneration of motor end plate.The function status of motor end plate reflects the muscles'.Domestic and foreign scholars have done a great deal of researches on the peripheral nerve injury in recent years. The recovery of nerve function is still not satisfactory despite the progress that made. Studies have found that methylcobalamin can promote a major component of myelin - the synthesis of lecithin, and can participate in synthesis of the neurotransmitter acetylcholine(ACh) to promote axonal rotation and axon regeneration in the treatment of diabetic peripheral neuropathy, especially the effective in treatment has been confirmed by animal experiments and clinical. However the effect and mechanism of recovery after nerve injury regeneration of skeletal muscle and motor end plate are less reported, especially in methylcobalamin on the motor end-plate acetylcholinesterase (AChE) and the change of acetylcholine receptor (AChR).In this study, therefore, the model of injured sciatic nerves on Wistar rats was constructed, which is treatment with methylcobalamin. We investigate the mechanism of methylcobalamin on promoting the regeneration of motor end plate with injured peripheral nerves through the change of nerve electrophysiology , the muscle wet weight, the shape of MEP, the content of acetylcholinesterase and acetylcholine receptors at different time after the treatments. And provide a theoretical basis for the treatment of neurological disorders.Methods:90 adult male Wistar rats(250—300g)were randomly divided into 2 groups:Group A,Methylcobalamin treated group and Group B,Physiological saline solution control group.To make and prepare the nerve injury model by clamping the rat sciatic nerve.The animal's consciousness recovered after about 2-3 hours since the operation finished, did local injection of drug. Injected Methylcobalamin 400μl /kg to Group A everyday, and injected the equivalent physiological saline to Group B everyday. 15 rats were taken randomly from group A and group B respectively in the first,the fourth and the eighth week after the operation,appraises the nerve function through the determination nerve conduction velocity. The gastrocnemius muscle is dissected and the wet weight is weighed by electron balance. Stained the muscular tissue by gold chloride to observe the change of MEP by using light Microscope, stained by AChE dyeing to observe the change of content of AChE and make an optical density measurementstained by Biosens Digital Imaging System, stained by AChR fluorescence dyeing to observe the change of acetylcholine receptor, all the results were analysed statistically.Results: 1, in the first week after the surgeries, the feet of rats had visible ulcer, and stand difficultly. Nerve conduction velocity showed no statistical significance (P>0.05). The wet weight of gastrocnemms muscle in Group A and Group B showed no statistical significance (P>0.05). The MEP became regressive in both groups ,the branch of Axon terminal is decrease and there was no evident difference.AChE staining showed the content of AChE reduced and there was not statistically significant between two groups for analysis of photo density (P>0.05).The shape of ACHR is incomplete and folds fewer. 2 , in the 4th week after the surgeries,Group A seemed better than Group B .Rats had two side missmatch walking and limping in Group B, nerve conduction velocity had statistical significance(P<0.05). The wet weight of gastrocnemius muscle in Group A and Group B had statistical significance(P<0.05). In group A,the number of MEP was increasing,the staining became deeper.In group B,the number increasing was not obviously, the staining was light and the shape was irregularity.AChE staining showed the number increasing was obviously only in Group A.The analysis of photo density of the MEP in two groups had statistical significance(P<0.05).The shape and the fold of AChR is more complete than group B,but less than normal. 3, in the 8th week postoperative,two sides walking were concordance in Group A and the limping could still be observed in Group B.The nerve conduction velocity gradually recovered in Group A, it has the statistical significance between the two groups (P<0.01).The wet weight of gastrocnemius muscle in Group A and Group B has obviously statistical significance (P<0.01). AChE staining showed that the number of MEP was more in Group A than that in Group B.The analysis of photo density of the MEP in two groups has significant statistical significance(P<0.01).The shape and the fold of AChR is nearly normal in groupA,but Group B is also irregular.Conclusions:1, Methylcobalamin could slow down the degeneration of motor end-plate after the peripheral nerve injuries,and promote the regeneration of the end-plate.2, Methylcobalamin could postpone the decline of natural weight of skeletal muscle after the nerve damage.3, Methylcobalamin could increase the contents of the acetylcholinase and the mature AChR receptor on the MEP , promote the restore of peripheral nerve after the injuries.4, Methylcobalamin could accelerate the functional recovery of nerve conduction after the peripheral nerve injuries.