The development of nerve-muscle junctions in Rana catesbeiana tadpoles

Abstract

The physiological properties of developing nerve-muscle junctions in Rana catesbeiana tadpoles are described. Developing neurons at different stages of ontogeny formed functional synaptic connections with a section of tail muscle implanted in place of the hind limb bud. Transmission is quantal in nature, sensitive in normal ways to calcium and magnesium concentrations, and conforms to a Poisson distribution. The quantal content is initially low and increases with development. Mepp's occur randomly and have low frequencies which increase slightly with development. The size of a single quantum of transmitter does not change during development. The muscle fibers are multiply innervated, resulting in Epp's with distinct peaks and complex skewed mepp amplitude histograms. No significant increases were observed in the level of differentiation of the developing motor neurons as a result of their having innervated a portion of mature tail muscle. The numbers of developing motor neurons increased in the experimental lateral motor column, and a lag in their maturity was observed relative to motor neurons in the control lateral motor column.