The characteristics of median nerve compound nerve action potential at different post injury and repair intervals and their correlation with nerve regeneration in rats

Abstract

Objective To explore the characteristics of compound nerve action potential (CNAP) after rat median nerve transection and repair,and their correlation with neuromorphometry at various time points. Methods The median nerve was transected and sutured at mid-arm level. At various time points from 2 to 12 weeks postoperatively,CNAP recording was performed and the median nerve was harvested for morphological examination. Results CNAP could be recorded at 2 weeks after nerve repair. The CNAP amplitude,the area below the curve (Area) and conduction velocity (CV) of regenerated nerve were significantly lower than those of control group (P＜0.01). From 2 weeks to 6 weeks postoperatively,CNAP latency (Lat) was obviously longer than normal (P＜0.05). From 2 weeks to 8 weeks postoperatively,CNAP stimulus intensity (threshold intensity and the supramaximal stimulation intensity,THI and SSI) was significantly lower than that of the control group (P＜0.01). First peak amplitude (FPA),peak-peak amplitude (PPA),Area and CV of CNAP increased with time,while parameters such as Lat,THI and SSI decreased over time in regenerated median nerve. Regenerated axons could be seen at 2 weeks after nerve transection and repair. More and more regenerated axons were seen with the lapse of time. There was a strong positive correlation between CNAP amplitude and the number of myelinated nerve fibers,with a 0.953 correlation coefficient. Linear regression analysis revealed the existence of a linear relationship. The maturity of regenerated nerve at 8 weeks reflected by myelin sheath thickness was close to that of a normal median nerve. Conclusion CNAP recording is a valuable tool to evaluate the extent of early nerve regeneration after nerve suture repair. There might exist a linear relationship between CNAP amplitude of normal median nerve and the number of myelinated nerve fibers. CNAP parameters are inclined to stabilize and nerve myelin sheath maturation is close to normal 8 weeks postoperatively. Key words: Median nerve; Nerve regeneration; Compound nerve action potential