Muscle spindle control during locomotor movements generated by the deafferented spinal cord

In acute spinalized (Th 12) cats, treated with DOPA, curarized or with all lumbosacral dorsal roots transected, stepping patterns were elicited in the hindlimbs by continuous electrical stimulation of the dorsal roots. Single primary endings in dorsal root filaments or single gamma and alpha efferents in muscle nerve filaments from flexors and extensors were recorded together with the efferent nerve activity to various hindlimb muscles. The experiments showed a clear coactivation of the intra- and extrafusal system to the same muscle. The alpha efferent discharges typically started with a very short first interspike interval. It is concluded that there exists a central spinal alpha-gamma-linkage for locomotion in the hindlimbs.