Metachronal propagation of motoneurone burst activation in isolated spinal cord of newborn rat.

Adequate locomotor and postural activity in mammals results from the coordinated activation of assemblies of spinal cord networks. In order to assess the global functioning of spinal circuitry, multisite recordings were made from an isolated spinal cord preparation of the newborn rat. Motor activity, elicited in a disinhibited network by bath-applying strychnine (glycinergic blocker) and bicuculline (GABAergic blocker), consisted of slow spontaneous bursting. Under these conditions, the recorded bursts were coordinated in 1: 1 relationships at all segmental levels. For each cycle, a leading segment initiated the activity that then propagated in a metachronal way through adjacent segments along the length of spinal cord. There was both regional non-linearity and directional asymmetry in this burst propagation: motor bursts propagated most rapidly in the thoracic spinal cord and the rostro-caudal wave travelled faster than the caudo-rostral one. Propagation involved both long projecting fibres and local intersegmental connections. These results suggest that the mammalian spinal cord contains propriospinal pathways subserving a metachronal transmission of motor information and that normally it may be involved in coordinating various parts of the body. The simple model developed here could be useful in unravelling more general mechanisms of neuronal circuit coupling.