Importance of pathway formation for nodal sprout production in partly denervated muscles.

Experiments were carried out to investigate possible factors controlling nodal sprout growth in partly denervated mouse gluteal muscles. Pretreatment of the muscle with botulinum toxin for up to 20 days, which produces denervation-like change and elicits terminal and nodal sprouting, increased reinnervation by terminal sprouting after partial denervation but did not alter the rate of reinnervation by nodal sprouts. This implies that nodal sprout growth is not limited by the development of an adequate growth stimulus from denervated muscle. A disto-proximal gradient of degeneration was observed in denervated intramuscular nerves in the electron microscope, suggesting that nodal sprout growth may be modulated by the availability of endoneurial pathways sufficiently degenerated to permit reinnervation by nodal sprouts, although the initial outgrowths from nodes of Ranvier may appear in response to a growth stimulus from denervated muscle.