Periodical assessment of electrophysiological recovery following sciatic nerve crush via surface stimulation in rats

When evaluating peripheral nerve regeneration, electrophysiological test is recognized as an optimal assessment, which is a quantitative, objective, and direct evidence reflecting function as compared to morphological examinations. In murine models of nerve regeneration, however, it remains a challenge to record compound muscle action potentials (CMAPs) periodically and non-invasively, i.e., with no insult to the nerve. In the present study, we recorded CMAPs in the gastrocnemius muscle weekly until 8 weeks after sciatic nerve crush by stimulating the nerve in a surface manner, and the electric stimuli were delivered to the skin between ischial tuberosity and major trochanter using bipolar hook electrodes. The CMAPs were reproducibly recorded in this way from 3 weeks post-injury, and both amplitude and latency were well correlated to post-operative time. Furthermore, a strong positive correlation was observed between CMAP amplitude and sciatic function index (SFI), a well-recognized assessment for sciatic nerve function. CMAP recordings by direct nerve stimulation at 8 weeks post-injury showed no significant difference in amplitude compared to surface stimulation, but the peak latency was relatively longer than the latter. This study indicated that non-invasive surface stimulation-based periodical recording of CMAPs was a practical electrophysiological approach to monitor the progression of peripheral nerve regeneration in murine models.