The Effect of Nerve Intervention in Spontaneous Activities and Muscle Fiber Type

Background: Following certain types of nerve injury, denervation potential is one of the types of spontaneous activities recorded from the denervated muscle. Fibrillation potentials (Fib. P) and positive sharp waves (PSW) are the typical potentials that are thought to disappear following nerve recovery.

Histological examination revealed changes in response to surgical intervention and correlated with denervation status.

Methods: We examined whether the extent of nerve damage could be estimated using four models of femoral-nerve damaged rats (cut, half-cut, crush, cut-and-suture models), and analyzing spontaneous potentials. The number of firings of the potential and the waveform were analyzed. With respect to waveforms, in addition to Fib.P and PSW, initial negative Fib.P (waveform of inverted Fib.P, first phase negative, and second phase positive are assumed to be reverse Fib.P), three-phase waves, multiphase waves (more than four-phase), and giant potentials (amplitude over 200 μV regardless of waveform) were classified.

In addition, ATPase muscle-fiber staining was used to indicate denervation status and muscle-type grouping. ATPase-stained muscle fibers were classified into muscle types using Brooke’s method. As a quantitative tissue evaluation, a microscopic photograph (magnification 100×) at the central part of each specimen was prepared, and the number of fibers of each type in the range of 400 × 400 μm was measured.

Results: In all means of surgical intervention, the frequency of firing peaked on the third day every postoperatively, and showed a decreasing trend thereafter. In the cut group, the firing frequency tended to slow with time, and ignition was observed even at eight weeks. Total firing potentials were graphed for each individual pattern(Figure 1). Denervation potentials such as Fib. P, reversed-Fib. P, and PSW peaked on the third day following injury, and disappeared in the eighth week following injury in all groups except the cut group. On the contrary, if these symptoms had persisted for the duration of the eight weeks, it might have indicated that a dominant nerve was damaged.

In the histological examination,the stainability declined with time in the cut group, and in other groups also changed according to the surgical intervention(Figure 2). In the cut group, typeⅡc was seen from the first week, and increased markedly up to the eighth week. Type I significantly increased in the cut and suture group from the fourth to the eighth weeks, and type I fiber presence also increased slightly.Type Ⅱc appeared at week four and decreased with the increase of typeⅠ and Ⅱa. It was thought that reinnervation occurred due to nerve regeneration by suturing, and muscle-type grouping occurred.

Conclusion: Spontaneous activities in damaged nerves reflect the denervation status to some extent. Histological studies indicated that the degree of stainability with ATPase staining demonstrated denervation status quite well. Also,Muscle type grouping could be seen from the denervated muscle.Clinically, there is limited research focusing on spontaneous activities and muscle-type grouping in nerve-muscle grafting or nerve transplant surgery. It may useful to consider the fiber type proportion of donor musle used in nerve-muscle grafting to reduce the reinnervation time.