Exogenous electrical nerve stimulation has been reported to promote nerve regeneration.Our previous study has suggested that endogenous automatic nerve discharge of the phrenic nerve and intercostal nerve has a positive effect on nerve regeneration at 1 month postoperatively,but a negative effect at 2 months postoperatively,which may be caused by scar compression.In this study,we designed four different rat models to avoid the negative effect from scar compression.The control group received musculocutaneous nerve cut and repair.The other three groups were subjected to side-to-side transfer of either the phrenic (phrenic nerve group),intercostal (intercostal nerve group) or thoracodorsal nerves (thoracic dorsal nerve group),with sural nerve autograft distal to the anastomosis site.Musculocutaneous nerve regeneration was assessed by electrophysiology of the musculocutaneous nerve,muscle tension,muscle wet weight,maximum cross-sectional area of biceps,and myelinated fiber numbers of the proximal and distal ends of the anastomosis site of the musculocutaneous nerve and the middle of the nerve graft.At 1 month postoperatively,compound muscle action potential amplitude of the biceps in the phrenic nerve group and the intercostal nerve group was statistically higher than that in the control group.The myelinated nerve fiber numbers in the distal end of the musculocutaneous nerve and nerve graft anastomosis in the phrenic nerve and the intercostal nerve groups were statistically higher than those in the control and thoracic dorsal nerve groups.The neural degeneration rate in the middle of the nerve graft in the thoracic dorsal nerve group was statistically higher than that in the phrenic nerve and the intercostal nerve groups.At 2 and 3 months postoperatively,no significant difference was detected between the groups in all the assessments.These findings confirm that the phrenic nerve and intercostal nerve have a positive effect on nerve regeneration at the early stage of recovery.This study established an optimized animal model in which suturing the nerve graft to the distal site of the musculocutaneous nerve anastomosis prevented the inhibition of recovery from scar compression.