Locomotor-like activity generated by the neonatal mouse spinal cord.

This report describes locomotor-like activity generated by the neonatal mouse spinal cord in vitro. We demonstrate that locomotor-like activity can be produced either spontaneously or by a train of stimuli applied to the dorsal roots or in the presence of bath-applied drugs. Calcium imaging of the motoneuron activity generated by a train of dorsal root stimuli revealed a rostrocaudally propagating component of the optical signal in the anterior lumbar (L1-L3) and in the caudal segments (S1-S4). We hypothesize that this spatio-temporal pattern arises from a rostrocaudal gradient of excitability in the relevant segments. Our experiments suggest that left/right reciprocal inhibition and NMDA-mediated oscillations are not essential mechanisms underlying rhythmogenesis in the neonatal mouse cord. Finally, our data are discussed in the context of other models of locomotion in lower and higher vertebrates.