Neural dependence and independence of myotube production in chicken hindlimb muscles.

Chicken embryos were paralyzed by repeated injections of the neuromuscular blocking agent d-tubocurarine, from the fourth day in ovo until sacrificed. This treatment affected the late but not early stages of myogenesis. The production of the initial generation(primary) of myotubes was unaffected whereas, in contrast, the acquisition of subsequent generations (secondary) of myotubes was totally inhibited. The elongation and growth of primary myotubes proceeded normally although their differentiation was retarded. An atrophy of these myotubes was not observed even in Day 17 embryos. It is concluded that the factors regulating myogenesis change as the muscle matures.