Formation of the central pattern generator for locomotion in the rat and mouse

It is well known that in the neonatal rat spinal cord preparation, alternat ing rhythmic bursts in the left and right ventral roots in a given lumbar s egment can be induced by bath-application of N-methyl-D-aspartate or 8-hydr oxytryptamine. Alternation between L2 and L5 ventral roots on the same side , representing the activity of flexor and extensor muscles, respectively, c an be observed as well. In the prenatal period in the rat, alternation betw een the left and right ventral roots is established between embryonic day ( E) 16.5 and E18.5, The alternation between the LS and L5 ventral roots emer ges at E20.5, Recent findings show that locomotor-like rhythmic activity wi th similar characteristics can be induced in the neonatal mouse preparation . In the lumbar spinal cord in the neonatal mouse, it is likely that the rh ythm-generating network is distributed throughout the lumbar region with a rostro-caudal gradient, a situation similar to that in the neonatal and fet al rat spinal cord. With this review we hope to highlight the dramatic chan ges that neuronal networks generating locomotor-like activity undergo durin g the prenatal development of the rat. Moreover, the distribution of the ne uronal network generating the locomotor rhythm in the neonatal rat and mous e spinal cord is compared. (C) 2001 Elsevier Science Inc.