| ObjectiveInvestigate the effect and mechanism of prolonged denervation on axonregeneration and functional recovery,to provide a theoretical basis for furtherexploration of preventing prolonged denervation and promoting axon regenerationand functional recovery.Methods1.40female SD rats were randomly divided into four groups, i.e.Immediatelysuture after injury (control group),1-month suture after injury (1-month group),3-month suture after injury(3-Month group),6-month suture after injury(6-monghtGroup). The biceps brachii muscle and musculocutaneous nerve denervated modelwas built as follows.The right side upper trunk of brachial plexus was avulsed,andMusculocutaneous nerve was transected.The distal stump of musculocutaneousnerve was ligated,embedded in the pectoralis minor muscle.Then the distalnerve,then the musculocutaneous nerve and biceps were denervated.2.4rats in Each group were randomly selected at corresponding timepoints(immediately,one month, three months,six months after injury),the survivaland proliferation of Schwann cell in distal segment of the nerve was observed usingS-100and P-75immunohistochemical staining.The wet weight of biceps brachiimuscle of each rat was weighted and recorded.3. To the remaining6rats in each group,the C7posterior divisions werefreshly cut and its proximal stump was sutured to the denervated distalmusculocutaneous nerve at corresponding time points after injury(immediately,onemonth,three months, six months).4. The recovery of right elbow flexion fuction of each rat was evaluated afternerve anastomosis.3months after N-N sutures, muscle wet weight and HE stain,electrophysiology of right biceps brachii muscle was measured,myelinated axon regenervation and neuromusclar (N-M) junction formation in the distal stump wereobserved.Results1. S-100protein staining showed abundant S-100expression in the axons ofmusculocutaneors nerve in control group,1-month group showed moderateexpression,3-month group and6-month group did not expressed any.Control groupmusculocutaneous nerve P75protein staining show moderate expression,1-monthgroup showed abundant expression,3-month group showed moderateexpression,6-month group did not expressed any.2. Denervated biceps showed muscular atrophy,and the wet weight of bicepsmuscle decreased by43%,48%and57%in1-month group,3-month group and6-month group respectively.However,no significant difference between theexperimental groups(P>0.05).3. After N-N suture,control group had a certain degree of recovery of elbowflexion at two week,and4week fully restored.In1-month group,elbow flexion had acertain degree of recovery at6week,which saw at8week in3-month group,but didnot see progressive improvement either.In6-month group,elbow flexion functionhad no recovery.4.3months after N-N suture,the CMAP,the muscle wet weight,the number ofregenerated axons progressively decreased in each experimental group withprolonged denervation and suture delay,significant difference were found in eachparameter(P<0.01).While betwween3-month group and6-month group,there was nosignificant difference in the myelinated axon regeneration(P>0.05).6-month groupdid not see any axon regeneration and neuromuscular junction.Conclusions1. Atrophy of denervated muscle occurs mainly in the first month,muscleatrophy is not obvious from1month to6month after denervated.When muscledenervated reach to6months,slowly progressive muscle atrophy still found.2. If the muscle denervated less than3months,The denervated muscle fiberstill able to accept new domination from regenerated axons,The muscle function recovery is depends on the quantity of regenerated axons.If the muscle denervatedmore than6months,the ability to accept newborn axons reinnervation of musclefibers declined,which may be the main reason leading to poor functional recovery.3. Axon regeneration depends mainly on the number of mature Schwann cells,not the number of activated and proliferated Schwann cells. |
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