Abstract: Objective To evaluate the morphological and functional changes of motor endplate in target muscles,and to explore the distribution characteristics and compensatory mechanisms after severing each nerve root of brachial plexus.Methods One hundred and twenty male SD rats were selected and randomly divided into five groups(n=24).The cutoff model of each root of the brachial plexus was built on the right side,and the left side was set up as the normal control group.At weeks 1,4,8,and 12 after amputation of each nerve root of brachial plexus,the target muscles of experimental sides and normal sides were tested by ways of acetylcholinesterase staining and single-fiber electromyography.The data of morphological and functional changes of motor endplate in target muscles were recorded and analyzed by SPSS21.0 software.Results In the group of cervical 5th or thoracic first nerve root amputation,there was no compensatory Jitter pattern found from target muscles,and the mean value of Jitter was significantly lower than that of the control side.Significant compensatory Jitter changes occurred after cervical 6th,7th,and 8th nerve root cutoff.The mean value of Jitter increased gradually in the 1-4 weeks after the cervical 7 nerve root cut,which was significantly higher than that in the control group(P<0.05),and then returned to normal after 8-12 weeks.The Jitter of the rest of the nerve roots was significantly lower than that of the control group(P<0.05).Among those groups of brachial plexus nerve root amputation,the distribution of MCD in the target muscles showing obvious compensatory changes only was found in cervical 7th group.In the group of cervical 5th or thoracic first nerve root amputation,the target muscle motor endplate area gradually expanded,acetylcholinesterase staining became lighter than before,and motor endplate gradually disappeared.The change of motor endplate in target muscle after cervical 6th nerve root resection was almost the same as that after cervical 8th nerve root cut:most of motor endplates disappear

Key words: Brachial plexus nerve root, Acetylcholinesterase staining, Single-fiber electromyography, Motor endplate