Partial denervation of amphibian skeletal muscle does not induce neuronal growth at the node of Ranvier

Following partial denervation of a striated muscle sprouting occurs at the nodes of Ranvier and terminal arborizations of the intact motor neurons. We studied the sprouting response of intact frog (Rana pipiens) motor neurons to partial denervation of the cutaneous pectoris muscle (CP). In the 5-19 days following partial denervation of the CP muscle, tetranitroblue tetrazolium-stained motor neurons exhibited sprouting. However, the mixed response of both nodal and terminal sprouting characteristic to mammalian muscle was replaced by a preferential response of only terminal sprouting. Histological examination showed that in many cases these terminal sprouts appeared to reinnervate abandoned junctional sites on adjacent denervated fibers. Given that nodal sprouting failed to occur for the duration of the experiment, these preliminary results suggest that the cues responsible for nodal sprout formation in the amphibian may differ from those in the mammal.