Functional denervation in the soleus muscle of dystrophic mice

The ability of dystrophic soleus muscle fibers to generate action potentials in response to supramaximal nerve stimulation was studied with intracellular microelectrodes in mice of the Bar Harbor 129-ReJdy strain. In experiments conducted in vivo at either 23 or 37 C, about 55% of the fibers examined were abnormal in their ability to generate action potentials. Some of these fibers showed no detectable response to stimulation of the motor nerve, whereas in others, abortive spikes or localized end-plate potentials were recorded. The proportion of fibers showing very small or no electrical response increased when recordings were made away from the end-plate zone. Reinnervated normal muscle fibers examined 1.5 months after microcauterization of the end-plate region often responded to nerve stimulation with abortive spikes. “Functional denervation” is discussed in terms of presynaptic and postsynaptic defects.