Brief Electrical Stimulation Promotes the Speed and Accuracy of Motor Axonal Regeneration

TLDR

Functional recovery after peripheral nerve injury is often poor because axons regenerate into inappropriate pathways. The study aims to assess how nerve transection affects regeneration speed and motor‑sensory specificity, to test whether electrical stimulation accelerates axonal growth and correct muscle reinnervation, and to elucidate its mechanism. The authors used retrograde neurotracers fluorogold and fluororuby to label motoneurons regenerating into muscle and cutaneous pathways, and investigated the cellular mechanisms of electrical stimulation. Electrical stimulation for 1–2 weeks at 20 Hz shortened the 10‑week regeneration period to 3 weeks, accelerated preferential motor reinnervation, and its effect is mediated by enhanced growth programs in the cell body, indicating a promising therapeutic strategy.

Abstract

Functional recovery is often poor despite the capacity for axonal regeneration in the peripheral nervous system and advances in microsurgical technique. Regeneration of axons in mixed nerve into inappropriate pathways is a major contributing factor to this failure. In this study, we use the rat femoral nerve model of transection and surgical repair to evaluate (1) the effect of nerve transection on the speed of regeneration and the generation of motor-sensory specificity, (2) the efficacy of electrical stimulation in accelerating axonal regeneration and promoting the reinnervation of appropriate muscle pathways by femoral motor nerves, and (3) the mechanism of action of electrical stimulation. Using the retrograde neurotracers fluorogold and fluororuby to backlabel motoneurons that regenerate axons into muscle and cutaneous pathways, we found the following. (1) There is a very protracted period (10 weeks) of axonal outgrowth that adds substantially to the delay in axonal regeneration (staggered regeneration). This process of staggered regeneration is associated with preferential motor reinnervation (PMR). (2) One hour to 2 weeks of 20 Hz continuous electrical stimulation of the parent axons proximal to the repair site dramatically reduces this period (to 3 weeks) and accelerates PMR. (3) The positive effect of short-term electrical stimulation is mediated via the cell body, implicating an enhanced growth program. The effectiveness of such a short-period low-frequency electrical stimulation suggests a new therapeutic approach to accelerate nerve regeneration after injury and, in turn, improve functional recovery.