Neurotrophic control of RNA synthesis in amphibian striated muscle.

When frog sartorius muscles are incubated in culture for 3 days, a 98% increase in RNA synthesis by the muscles is seen. A portion of this increase (60--100% in different experiments) is prevented by the presence of a 2 cm distal nerve stump left attached to the muscle, or by the addition to the culture medium of nerve and spinal cord extracts from frog, rat or cow. The effect of the nerve stump and the extract is seen under conditions of neuro-muscular blockade by 50 mg/l gentamicin sulfate present in the culture medium. Autoradiography of 1 micrometer sections of muscles previously labeled with [3H]uridine shows that isotope incorporation is largely confined to muscle fibers rather than connective tissue. Muscles cultured for 3 days display normal action and resting potentials either in the presence or absence of extract. The results are discussed in terms of control of muscle RNA synthesis by substances present in motor neurons.