A new mutant mouse with motor neuron disease

The present study was undertaken to examine the abnormality in motor function of newly found mutant mice electrophysiologically. It was found that their motor nerve fibers progressively fail to conduct action potentials, while impulse conduction in the sensory fibers remains intact. The conduction block of motor fibers proceeded in the proximo-distal direction. Excitation of the motor fibers was blocked by raising the extracellular Ca2+ or Mg2+ concentration in vitro. It is concluded that this new mutant mouse has a motor neuron disease of the 'dying-forward' type.