The effect of prolonged, reversible block of nerve impulses on the elimination of polyneuronal innervation of new-born rat skeletal muscle fibers.

The soleus muscle was reversibly paralyzed in 9- and 10-day-old rats by implantation of a plastic plug containing slowly releasable tetrodotoxin under the epineurium of the sciatic nerve. After different periods of paralysis we determined the frequency of polyneuronally innervated fibers in the muscle by intracellular recording of end-plate potentials to nerve stimulation. During the first 2–4 days of nerve block the elimination of polyneuronal innervation, occurring in rat muscles of this age, proceeded nearly as normally. After longer periods of block there was an increased frequency of polyneuronally innervated muscle fibers presumably due to motor nerve sprouting induced by the paralyzed muscle.