[Responses of medullary neurons to stimulation of locomotor and inhibitory loci in the brain stem of the cat].

The medullary locomotor point (L) and the pontine inhibitory point (I) were found in mesencephalic decerebellate cats. Repetitive (60/s) microstimulation of L elicited stepping of forelimbs which terminated during repetitive microstimulation of I. Responses of neurons were evoked applying 1.5 s-1 single or paired stimuli to L or a train of 2-4 stimuli to I, the interstimulus interval being 2 ms. Medial neurons (N-301) gave PSPs or action potentials of 1 stimulation three times as often as to L stimulation. Contrary, lateral neurons (N-166) responded two times as often as to L stimulation. IPSPs were recorded in both groups of neurons two times as seldom as EPSPs. In medial neurons IPSPs were produced mainly by I stimulation. I stimulation did not evoke usually IPSPs in neurons excited from L. Possible mechanisms of termination of stepping due to I stimulation are discussed.