Neurons of upper cervical segments responding to stimulation of the bulbar locomotor strip

Synaptic responses of single neurons to stimulation of the bulbar "locomotor strip" were recorded extracellularly from superior cervical segments in mesencephalic cats. With a strength of stimulation of about 30 μA these responses usually had a latent period of 2-7 msec and they arose in neurons located at a depth of between 2 and 4 mm from the dorsal surface (Rexed's laminae V-VIII). These neurons could not be excited antidromically by stimulation of the lumbar or lower cervical segments. However, antidromic responses could be evoked by stimulation of a region located 3-5 mm caudally to the site of recording. It is suggested that neurons of segments C2 and C3 excited by stimulation of the locomotor strip are components of a cell column along which activity spreads polysynaptically in the direction of spinal stepping generators.