Changes of denervated skeletal muscle and motor endplate after nerve repair with different intervals of delay:an experimental study

Abstract

Objective To investigate the changes of denervated skeletal muscle and motor endplate after nerve repair with various intervals of delay,and discuss the best timing for nerve repair. Methods Gastrocnemius muscle denervation was established in 36 SD rats which were randomly divided into 6 groups based on different intervals of delay for surgical nerve repair(0,2,4,6,8,10 weeks),with 6 each.All the manipulations were done on the right hind limbs while the unoperated left hind limbs served as control.Six weeks after nerve repair,muscles were harvested for evaluation.Results When nerve repair was carried our within 0 to 4 weeks of denervation,muscle wet weight continued to drop but showed to significant statistical difference between the groups(P>0.05).Muscle weight showed a remarkable drop when nerve repair was done after a 4week delay,and then maintained at a certain level.Diameter and cross sectional area of muscle fibers continued to decline.When the injured nerve was repaired within 2 weeks,the CCRP(calcitonin gene-related peptide)gray scale of motor endplate was not significantly different from that of the control side(P>0.05).The gray scale of CGRP of motor endplate in groups when nerve repair was done after 4 to 6 weeks was significantly lower than that in the group when nerve repair was done within 2 weeks(P<0.05).In the group of nerve repair with 8-week delay,CGRP gray scale further-declined,being significantly different(P<0.05)compared to that of the 6 week repair group.Ultrastruetural changes were in agreement with light microscopic changes.Conchlusion Nerve repair done within 2 to 4 weeks of injury lead to better results.Although muscle atrophy was less likely to be reversible when nerve repair was delayed for 6 weeks,there were still indications for nerve repair since some parameters still remained at a certain level. Key words: Motor endplate; Rats; Denervated muscle; Nerve repair