ISDN2012_0291: Neural cells reprogrammed from non‐ectodermal cells

Molecular Neurobiology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA The spinal cord plays a central role in generating both the simple and complex patterns of motor activity needed for locomotion. It also processes and relays sensory information from the body to the spinal motor system and other CNS structures involved in somatosensation. Recent developmental studies have provided an outline of the key pathways that control the specification, organization and functional properties of the neurons that contribute to sensory-motor circuits in the spinal cord. Using a comprehensive approach that combines genetics, neuroanatomical, electrophysiological and behavioural analyses we have begun to assess the contribution that molecularly identified neuronal cell types make to the control of movement in mammals. We have characterized various populations of the spinal interneurons including dI6, V0, V1, V2b and V3 interneurons. Our studies show that each interneuron class controls a distinct facet of the motor output of the spinal cord that is needed for locomotion. IN so doing these studies reveals that the spinal locomotor circuitry has an underlying modular organization. V0 interneurons control left-right stepping. Excitatory V3 commissural interneurons are required for the generation of robust and balanced motor rhythm. V1 interneurons generate inhibitory neuron cell types that include Renshaw cells and Ia INs, and they control the cadence of the step cycle. More recently we have identified another class of inhibitory interneuron that together with V1 cells controls all flexor–extensor behaviors. Both cell types are present in the spinal cords of aquatic vertebrates arguing that these interneurons were recruited and reconfigured during vertebrate evolution to control the primitive fin and limb movements.