[Activity of propriospinal neurons of segments C3 and C4 during "fictive locomotion" in the cat].

The activity of C3-C4 propriospinal neurons was recorded during "fictitious locomotion" of forelimbs in immobilized decerebrated cats with the spinal cord transected at the lower thoracal level. The neurons were identified by the antidromic responses to stimulation of the lateral funiculus in the C6 segment. Most of the neurons (70%) were antidromically activated also from the lateral reticular nucleus. The discharge frequency of most neurons was rhythmically modulated in correlation with the motoneuron activity during "fictitious locomotion", i.e. in the absence of any rhythmical signals from the limb receptors. The cooling of the rostral area of the cervical enlargement abolished both the generation of the locomotor rhythm and the rhythmical activity of the propriospinal neurons. Therefore intraspinal mechanisms controlling the forelimb activity are the main source for rhythmical modulation of the C3-C4 propriospinal neurons.