Neonatal Circuits

This article describes the organization of motor circuitry in the neonatal spinal cord. The focus is on locomotor-like activity expressed by the isolated spinal cord in vitro and the interneuronal networks responsible for this behavior. The coordination between thoracolumbar segments controlling the hind limbs and sacrocaudal segments controlling tail movements is described and interneurons responsible for this coordination are discussed. The development of two classes of spinal interneurons – Renshaw cells and 1a inhibitory interneurons – that are thought to be involved in locomotor activity is then considered. Finally, new genetic approaches to the organization of motor circuitry in the neonatal spinal cord are reviewed.