Spinal cord stimulation in chick embryo: Effects on development of the posterior latissimus dorsi muscle and neuromuscular junctions

The purpose of this work was to study whether or not stimulation of spinal cord at a critical stage of development in chick embryo would result in a modification of neuromuscular differentiation. The electrodes were implanted anteriorly and posteriorly to the level of motor innervation of the wing. Stimulation was delivered from the 10th day of development, and the posterior latissimus dorsi muscle was studied at Day 14 for cholinesterase activity and innervation or at Day 17 for mechanical activity. In normal development of chick embryo, the posterior latissimus dorsi differentiates into a fast muscle whose fibers have a single end plate. In spinal cord-stimulated embryos, we observed a multiplicity of sites of cholinesterase activity and multi innervation in the posterior latissimus dorsi muscle fibers. Moreover, speeds of contraction and relaxation were slower than in control muscles. These results show that electrically induced activity of motoneurons at a critical stage of embryogenesis modifies the development of the neuromuscular system. Possible explantions of this phenomenon are discussed.