Changes in segmental and propriospinal reflex pathways during spinal locomotion

In high spinal immobilised cats the transmission in segmental reflex pathways from cutaneous afferents and in descending propriospinal pathways from forelimb afferents to lumbar motoneurons was investigated during fictive locomotion. Synaptic responses evoked via these pathways showed basically the same dependence on the phase of the step cycle—generally EPSPs were favoured during the phase of activity of the corresponding motoneurons, while IPSPs (except for the early propriospinally mediated IPSP in FDL motoneurons) tended to increase or to occur during the phase of inactivity of the motoneurons. By this facilitation of excitatory influences and depression of inhibitory influences to motoneuron pools, the ‘locomotor generator’ may functionally support those muscles which are in their active phase, independently of the source of the stimulated afferents.