Some limitations of ventral root recordings for monitoring locomotion in the in vitro neonatal rat spinal cord preparation.

Studies of the in vitro neonatal rat spinal cord have used ventral root recordings, among other methods, to monitor locomotion. However, whether ventral root activity reliably indicates the presence of hindlimb stepping has not been established. In the present study, we use an in vitro spinal cord-hindlimb preparation to analyse lumbar ventral root recordings obtained while simultaneously observing coordinated stepping movements or rhythmic alternation of ankle flexor and extensor nerve activity. During locomotion ventral root patterns included: tonic activity, rhythmic left-right alternation with in-phase activity of ipsilateral roots, and rhythmic activity that was in-phase both bilaterally and ipsilaterally at different segmental levels. Ventral root transection during rhythmic activity demonstrated that ankle flexor and extensor nerve activity depended on motor units coursing through common lumbar roots in 31/39 hindlimbs. These findings suggest that ventral root recordings alone are not a reliable means of monitoring phasic hindlimb flexor and extensor activity during locomotion in the in vitro rat preparation.