[Corticofugal effects on interneuron segmental reactions of the ventral horn of the lumbar segments of the spinal cord in the cat].

Impulse activity of the lumbar ventral horn interneurons evoked by stimulation of afferent nerves of both hindlimbs is shown to be modulated (facilitated or inhibited) by descending volleys from the cerebral motor cortex. Facilitation was of short duration and did not exceed 35-40 ms. Duration of inhibition varied from 125 to 350 ms; in a few cases it lasted up to 500 ms. Polysynaptic reactions evoked in one and the same neuron by activation of different inputs were modulated differently: some of them could be depressed, while others--enhanced or unchanged. It is suggested that such differentiation is due to specific organization of these afferent inputs. Central latency of the test response was another main factor determining the type of its cortical modulation. Polysynaptic responses with a central delay less than 5 ms were facilitated or unchanged (in a few cases--depressed) while responses with central delay more than 5 ms were always depressed. Reactions with a latency more than 10 ms were depressed most deeply. Possible mechanisms and ways of transmission of corticofugal inhibition and facilitation are discussed.