Stimulated single fiber electromyography in the mouse: techniques and normative data

Area of Science:

• Neuroscience
• Physiology
• Biomedical Engineering

Background:

• Increasing need for sensitive methods to evaluate peripheral nervous system function in transgenic mouse models of human neuromuscular diseases.
• Neuromuscular junction (NMJ) dysfunction is often undetectable by standard morphological or functional assays.
• Development of advanced electrophysiologic techniques is crucial for accurate assessment of NMJ integrity.

Purpose of the Study:

• To develop and validate a method for stimulated single fiber electromyography (S-SFEMG) in mice.
• To assess the sensitivity of S-SFEMG in detecting NMJ dysfunction under various physiological conditions.
• To evaluate the safety factor of neuromuscular transmission in mouse models.

Main Methods:

• Developed and tested S-SFEMG in the gastrocnemius muscles of anesthetized mice.
• Assessed jitter by measuring mean consecutive latency difference (MCD) of single fiber responses to sciatic nerve stimulation (2 Hz).
• Evaluated the effects of core temperature, mechanical ventilation, and neuromuscular blocking agents (vecuronium) on jitter.

Main Results:

• Established normal mean MCD values (6-8 micros) in normothermic mice across different strains.
• Demonstrated that reduced core temperature significantly increased jitter.
• Showed that vecuronium administration progressively increased jitter and led to blocking, confirming S-SFEMG's sensitivity.
• Found that intubation and mechanical ventilation did not alter jitter values.

Conclusions:

• Validated S-SFEMG as a sensitive and reliable index of murine NMJ function.
• Highlighted the utility of S-SFEMG for studying neuromuscular transmission under diverse physiological states.
• Suggested the existence of a high safety factor for neuromuscular transmission at mouse NMJs.