Comparison of incremental with multipoint MUNE methods in transgenic ALS mice

Several methods of motor unit number estimation (MUNE) are in current use. Uncertainty still exists about which is preferable and how results obtained from one method compare to another. We studied changes with MUNE over time in the SOD1(G93A) transgenic mouse model of amyotrophic lateral sclerosis (ALS), using both incremental and multipoint methods. This mouse model of motor neuron degeneration is highly consistent, with a monotonic decline in motor neuron number starting at approximately 60 days of life. Five mice were studied four times each, starting at day 60 of life and approximately every 20 days thereafter, using both methods. Results were quite comparable for both methods, with the incremental method yielding slightly higher estimates of motor unit size, and hence smaller MUNEs. Correlations between the two methods were 0.71 for single motor unit action potential (SMUAP) amplitude and 0.95 for MUNE. In this model, therefore, both MUNE methods yield similar estimates and are equally effective at documenting progression of a lower motor neuron disorder.