Measuring Compound Muscle Action Potentials in Mouse Forelimb Muscles In Vivo

Secure an anesthetized mouse in a supine position. 

Subcutaneously insert the stimulating electrodes, aligning them with the nerve innervating the forelimb muscle.

Subcutaneously insert the recording electrode on top of the upper arm muscle, the reference electrode into the walking pads, and the ground electrode on the side.

Apply electrical pulses to stimulate the forelimb neurons, inducing a positive ion influx and action potential generation.

The action potential induces excitatory neurotransmitter release at the neuromuscular junction, leading to muscle fiber activation and contraction.

Record the combined response from all muscle fibers — the Compound Muscle Action Potential, or CMAP.

Apply maximal stimuli to ensure stimulation of all muscle fibers.

End the stimulation and determine the latency, the time delay between the initiation of the stimulus and the response.

Increased latency indicates decreased conduction speed due to neuronal demyelination.

Measure the CMAP amplitude; a decreased magnitude indicates the loss of functional neurons.