Denervation of newborn rat muscle does not block the appearance of adult fast myosin heavy chain.

Several observations, both in vivo and in vitro, have indicated that the development and maturation of mammalian skeletal muscle fibres is influenced by nerve-muscle interactions. Morphological maturation of newly regenerated adult mouse muscle fibers in an organotypic nerve-muscle culture system depends on the presence of spinal cord neurones. Sciatic nerve transection in newborn rats has been shown to modify the development of the histochemical and contractile properties of the denervated muscles. In addition, neural influences are important for the appearance of certain of the myosin small subunits. It has been proposed that the nerve also controls the changes in myosin heavy chain isozymes appearing during development. One such transition occurs in rat muscle where the neonatal form of myosin heavy chain is replaced by the adult form during the second post-natal week. Here we demonstrate that innervation of the rat gastrocnemius muscle (a fast-contracting muscle in the adult) is not required for the appearance of the adult form of myosin heavy chain.