Synaptic responses of propriospinal neurons to stimulation of the stepping strip of the dorsolateral funiculus in cats

Synpatic responses were recorded extracellularly from single neurons at levels T12-T13 in response to microstimulation of the stepping strip of the dorsolateral funiculus in the thoracic and cervical portions of the spinal cord in cats decerebrated at the precollicular level [4]. The latent periods of these responses increased when the distance between the stepping point and recording point exceeded 20 mm, and when two stimuli had to be applied in order to evoke responses. Axons of neurons respondingtrans-synaptically to stimulation of the stepping strip were located on the boundary between the lateral and ventral funiculi close to the gray matter. Antidromic responses of neurons sending their axons in the caudal direction were found on average in 37% of cases, provided that the distance between the recording and stimulation points did not exceed 40 mm. Half of the neurons which generated synaptic responses to stimulation of spinal stepping points could be excited also by a series of three to six stimuli, applied to the mesencephalic locomotor point [15]. It is suggested that the neurons discovered may participate in the spread of activity toward the generator of stepping movements of the hind limb.