Spontaneous elimination of nerve terminals from the endplates of developing skeletal myofibers.

The development of the motor innervation of a skeletal muscle was examined in the soleus muscles of young rats. At 11 days after birth, nearly three-quarters of the endplates of individual myofibers were innervated by more than one silver stained axon. Four days later, only about 9% of the endplates remained innervated by two or more terminals. The dramatic reduction in the number of axon terminals appeared to result in large measure from the retraction of all but one of the multiple terminals. An axon interpreted as undergoing retraction was characterized by a terminal oval enlargement believed to be the site of disassembly of the fiber.