Ubiquity of motor networks in the spinal cord of vertebrates.

In a recent paper, we found that it is possible to record motor activity in sacral segments in the in vitro neonatal rat spinal cord preparation. This motor activity recorded in segments that are not innervating hindlimbs is driven by the lumbar locomotor network. Indeed, compartimentalizations of the cord with Vaseline walls or section experiments, reveals that the sacral segments possess their own rhythmogenic capabilities but that in an intact spinal cord they are driven by the lumbar locomotor network. In this review, these recent findings are placed in the context of spinal motor network interactions. As previously suspected, the motor networks do not operate in isolation but interact with each other according to behavioural needs. These interactions provide some insight into the discrepancies observed in several studies dealing with the localization of the lumbar locomotor network in the neonatal rat spinal cord. In conclusion, the spinal cord of quadrupeds appears as an heterogeneous structure where it is possible to identify neuronal networks that are crucial for the genesis of locomotor-related activities.