On the Descending Control of the Lumbosacral Spinal Cord from the “Mesencephalic Locomotor Region”

Continuous stimulation (60 c/s) of a region below the inferior coliculus can induce locomotion on the treadmill of precollicular, postmammilar cats. This study aims at revealing what changes occur in the spinal cord, when the “locomotor region” is stimulated. This stimulation enables the cat to walk if the treadmill is moved. After controlling the threshold for evoking good locomotion, the cats were curarized. Stimulation at a strength that evoked walking prior to curarization induced a depression of inhibitory short‐latency reflex effects to α‐motoneurones from cutaneous, and high threshold muscular afferents without changing the direct excitability of α‐motoneurones. The threshold for evoking longlasting reciprocally organized discharges was lowered. The results suggest that the effects are induced by a slow fiber system, that releases the activity of the spinal stepping generating neurones. The results would be explained if the noradrenergic reticulospinal system was activated from the mesencephalic locomotor region.