GENESIS OF SPONTANEOUS RHYTHMIC MOTOR PATTERNS IN THE LUMBOSACRAL SPINAL-CORD OF NEONATE MOUSE

The isolated spinal cord of the neonatal mouse spontaneously generates two different motor patterns of continuous rhythmic bursting: one in lumbar ventral roots in earliest postnatal preparations (P0-2) and ano ther at the sacral level at later postnatal times (P3-5). Lumbar rhyth mic motor discharges clearly alternate on contralateral roots and are in a frequency range (approximate to 1 Hz) usually described for locom otor-like activity, while sacral motor sequences include mixed synchro ny and irregular bilateral alternation that differ from typical locomo tor-like activity. A significant decrease in the frequency and increas e in the duration of spontaneous rhythmic bursts occur between lumbar and sacral motor patterns. In quiescent preparations from both postnat al periods, perfusion with Mg2+-free medium systematically induces a r hythmic activity at both lumbar and sacral level. Temporal characteris tics of motor patterns under Mg2+-free medium are similar to spontaneo us rhythms. Activating NMDA receptor channels by diminishing their Mg2 + block appears to be an efficient way of decreasing the threshold for genesis of the spinal rhythm in mouse. Bath application of NMDA and n on-NMDA receptor antagonists blocks Mg2+-free-induced rhythmic activit ies in an irreversible or reversible manner, respectively. The effects of Mg2+-free medium and of glutamate antagonists provide evidence for the excitatory amino acid (EAA) dependence of both rhythmic motor pat terns. Finally, the possibility that the recording of two different mo tor patterns may reflect a rostrocaudal developmental process is discu ssed. (C) 1998 Elsevier Science B.V. All rights reserved.