SOME LIMITATIONS OF VENTRAL ROOT RECORDINGS FOR MONITORING LOCOMOTIONIN THE IN-VITRO NEONATAL RAT SPINAL-CORD PREPARATION

Studies of the in vitro neonatal rat spinal cord have used ventral roo t recordings, among other methods, to monitor locomotion. However, whe ther 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 steppi ng movements or rhythmic alternation of ankle flexor and extensor nerv e activity. During locomotion ventral root patterns included: tonic ac tivity, rhythmic left-right alternation with in-phase activity of ipsi lateral roots, and rhythmic activity that was in-phase both bilaterall y and ipsilaterally at different segmental levels. Ventral root transe ction during rhythmic activity demonstrated that ankle flexor and exte nsor nerve activity depended on motor units coursing through common lu mbar roots in 31/39 hindlimbs. These findings suggest that ventral roo t recordings alone are not a reliable means of monitoring phasic hindl imb flexor and extensor activity during locomotion in the in vitro rat preparation.