Facial nerve CMAP acquisition in mice: Protocol, normative data, reliability, and injury/repair model application.

PURPOSE: This study aimed to establish and validate a minimally invasive method for percutaneous compound muscle action potential (CMAP) recordings of the murine facial nerve, including normative values, reliability metrics, and biological sensitivity to nerve injury.

METHODS

Thirty adult C57BL/6 mice underwent bilateral facial nerve CMAP recordings using percutaneous needle electrodes placed at defined anatomical landmarks. Three repeated measurements (total n = 180) were obtained to assess intra-session reliability, while inter-side and inter-session reproducibility were evaluated in a subgroup of 25 animals over 30 days. CMAP amplitude, latency, and duration were analyzed using intraclass correlation coefficients (ICC), coefficients of variation (CV%), and minimal detectable change (MDC). Biological validity was tested in a facial nerve transection and microsurgical repair model (n = 10), with longitudinal recordings at baseline, 30, 60, and 90 days.

RESULTS

Mean CMAP amplitude was 10.0 ± 1.5 mV, latency 1.5 ± 0.2 ms, and duration 1.0 ± 0.1 ms. Intra-session reliability for CMAP amplitude and latency was moderate to good (ICC 0.61-0.81), with low variability (CV<15%), whereas inter-side and inter-session reliability varied across parameters. Inter-session amplitude reliability was moderate (ICC=0.59), with an MDC of approximately 2 mV. Facial nerve injury resulted in a significant reduction in CMAP amplitude on the injured side compared with contralateral control (main effect of side: F(1,18)= 40.1, p < 0.0001), followed by partial recovery over time (interaction p < 0.0001).

CONCLUSIONS

This study establishes a standardized protocol for murine facial nerve CMAP recording with moderate reliability and low variability. The method is well suited for detecting group-level functional changes and enables longitudinal assessment of facial nerve injury and regeneration.