Comparison between ventral spinocerebellar and rubrospinal activities during locomotion in the cat.

During fictive locomotion of the thalamic cat, rhythmic activity related to the efferent discharges in hindlimb nerves was found in rubrospinal neurons (Arshavsky et al., this issue). Since the movements were abolished by curarization, this modulation could not result from rhythmic peripheral inputs and had therefore a central origin. Taking into account the existence of spinal generators, it was suggested that ascending pathways transmit rhythmic activity from these spinal centers to the supraspinal ones. Preliminary results have been obtained for neurons of the ventral spinocerebellar tract (VSCT) recorded during fictive locomotion: (1) their discharge is rhythmically modulated at the periodicity of the locomotor rhythm; (2) their discharge pattern can be complex and variable in relation with the complexity and variability of the pattern of efferent activity in various muscle nerves of the ipsilateral hindlimb; (3) their responses to phasic afferent stimulation of the ipsilateral hindlimb are modulated in parallel with their locomotor-related activity. These results show that VSCT neurons convey information on the central spinal activity during locomotion, and suggest that these neurons contribute to the activity of lumbar-projecting rubrospinal neurons which have similar characteristics.