Expression Of Muscle-type AChR Subtypes In Donor And Recipient Muscles After Musculocutaneous Nerve Transection And Reconstruction Of Elbow Flexion In Rats

Objective: To explore the expression patterns of muscle-type AChR subtypes (ε-AChRand γ-AChR) in the recipient muscle (biceps brachii) and donor muscle (oblique part ofpectoralis major) after musculocutaneous nerve transection and reconstruction of elbowflexion, provide a scientific guidance for the prevention and treatment of donor andrecipient muscles atrophy.Methods:1. Experimental animals and groups: Forty-two adult Sprague Dawley rats,weight,200±50g, either male or female. The animals were divided into A, B, C and Dfour groups, of these, the B, C and D group were further divided into two groups, i.e Agroup (normal); B1and B2groups (2w post-, and4w post-musculocutaneous nervetransection); C1and C2groups (2w post-, and4w false post-reconstruction of elbowflexion); D1and D2groups (2w post-, and4w post-reconstruction of elbow flexion).Each group is comprised of6rats.2. Gross anatomy.3. Partial pectoralis major muscletransfer after musculocutaneous nerve transection for establishing an animal model ofreconstruction of elbow flexion.4. Muscle morphology was observed and muscle wetweights were assessed.5. ε-AChR and γ-AChR mRNA expression was detected by PCR.6.ε-AChR and γ-AChR protein expression was detected through western blot technology.Results:1. Gross observation: The oblique part of pectoralis major of a SD rat is longenough for suturing to the insertion of the biceps brachii tendon. This surgery did notinjury the blood vessels and nerves and could meet the requirements of the suture withouttension. After musculocutaneous nerve transection, the color of the biceps brachii musclefaded, the muscle mass shrunk, and the foraging movements were restricted progressively.After the oblique part of the pectoralis major was transferred for reconstruction of elbowflexion, the foregoing changes improved gradually. A little change of pectoralis majormuscle oblique part was noted before and after operation.2. Muscle wet weight: The group A muscle wet weight of the biceps brachii was0.38±0.01g, after musculocutaneous nervetransaction, the group B and group C compared to the group A, alleviated progressively;The group D compared to the group A, showed a graduall rebound after reconstruction ofelbow flexion, p <0.05. The group A muscle wet weight of the oblique part of pectoralismajor was0.37±0.01g, the group D1compared to the group A after reconstruction ofelbow flexion, with a decrease of2.70%, p <0.05; the group D2showed a reboundcompared to the group A, p>0.05.3. Expression level of the mRNA: The group Aexpression level of the ε-AChR in the biceps brachii and oblique part of the pectoralismajor were0.66±0.03and0.82±0.02respectively, no expression of γ-AChR. Theε-AChR expression in the biceps brachii, the group B and C compared to the group A weredeceased gradually, and the γ-AChR reexpression and with an increase gradually; Afterreconstruction of elbow flexion, the group D compared to the group B2, the ε-AChR wasobviously up-regulated expression and the γ-AChR was downregulated expression,Whereas the group C compared to the group B2showed the opposite response, p <0.05.The expression of the ε-AChR in oblique part of pectoralis major, the group D1and groupD2compared to the group A decreased by14.63%and1.22%respectively; group D1compared to group A, p <0.05, and group D2compared to group A, p>0.05; γ-AChRreexpressed as0.18±0.01in group D1, and group D2almost faded, Only0.01±0.01. Thegroup D2compared to group D1was obviously,decreased, p <0.05.4. Protein expressionlevel: The change patterns of the ε-AChR and γ-AChR protein expression in each groupwere the same as the mRNA expression at different time points, and the changes amplitudeof the protein expression at each time point were lower than that of the mRNA expression,except in the group A.Conclusions:1. The oblique part of pectoralis major muscle was used as a donor toestablish an animal model for reconstruction of elbow flexion is feasible and can improvebiceps brachii (recipient muscle) atrophy in SD rats.2. After musculocutaneous nervetransaction, the ε-AChR mRNA and protein expression in the biceps brachii weredecreased gradually, and the γ-AChR followed by upregulation; The expression changes ofthese two receptor subtypes were contrary in recipient muscle after reconstruction of elbow flexion.3. The reconstruction of elbow flexion surgery causes only transient abnormalexpression of γ-AChR and ε-AChR to donor muscle in rats.