Presynaptic mechanisms of the change in segmental responses accompanying the formation of the spinal locomotor generator in the cat

It is shown on unanesthetized immobilized decorticated cats that spinalization of the animal leads to depolarization of the central afferent terminals, decrease of early polysynaptic responses in motoneurons and dorsal root potentials (DRP) evoked by stimulation of the low-threshold cutaneous and muscle afferents, increase of early polysynaptic responses and DRP evoked by stimulation of high-threshold muscle afferents, reduction in the activity of intermediate nucleus interneurons mono- and polysynaptically connected with primary afferents, rise of the activity of interneurons di- and oligosynaptically connected with primary afferents. Injection of DOPA into spinal animals leads to opposite changes. Dependence between changes in the state of segmental neuronal apparatus and the level of spinal locomotor generator activity are discussed on the basis of the data obtained.