[Responses of neurons of the upper cervical segments of the spinal cord in the cat to stimulation of the locomotor region of the brain stem with different frequencies].

Synaptic responses of C2 and C3 neurons to stimulation of medullary or midbrain locomotor points were recorded extracellularly in mesencephalic cats. Neurons excited with a firing index of 0.4-0.6 at a stimulation frequency of 2 S-1 retained this index at frequencies of 20-60 S-1 too. Many neurons with the low firing index under the stimulation frequency of 2 S-1 increased it to 0.4-0.6 under high frequency. More than a half of neurons were excited by stimulation of both ipsi- and contralateral locomotor points; a quarter of units responded to stimulation of locomotor points both in the medulla and in the midbrain. The neurons under study were located at a distance of 1.8-4.2 mm from the dorsal surface of the spinal cord. Average latencies of responses with a firing index more than 0.5 were distributed between 2 and 30 ms with a mode of 2-8 ms. Long-latency responses had significant fluctuations of latency. A possible participation of the investigated neurons in the propagation of activity from the brain stem locomotor region to stepping generators in the spinal cord is discussed.