Coupling between lumbar and sacral motor networks in the neonatal rat spinal cord.

We have studied the rhythm-generating capabilities of the lumbar, sacral and coccygeal (Co) areas using an isolated spinal cord preparation of the newborn rat. The bath-application of a mixture of N-methyl-D-L-aspartate (NMA) and serotonin (5-HT) on the whole spinal cord induced a coordinated rhythmic activity that could be recorded from the lumbar to the coccygeal ventral roots. The phase relationships and mean burst duration between the activity in the rostral lumbar segments and the activity in the sacral segments was analysed. The direct activation of the sacral network, by using sections or by selective pharmacological activation, showed that these caudal segments possess their own rhythmogenic capability. By combining section experiments and compartmentation of the spinal cord, we demonstrated that a strong coupling exists between the lumbar and sacral motor networks. In addition, we found that in an intact spinal cord the activity of the sacral networks is driven by the lumbar networks. We have found that different modes of coordination between the lumbar and the sacral activity may occur. Finally, we have shown that the coupling between the lumbar and sacral networks can be modified by sensory inputs, suggesting that the spinal machinery could modulate and adapt the coupling of these two spinal networks.