Synaptic processes in neurons of the cervical enlargement of the cat spinal cord during stimulation of propriospinal pathways of the dorsolateral tract

Abstract

Responses of motoneurons and interneurons of the cervical enlargement of the cat spinal cord were studied by a microelectrode technique during selective stimulation of propriospinal fibers of the dorsolateral tract of the lateral white column. The long descending and ascending pathways were blocked by preliminary (10–16 days earlier) hemisection of the spinal cord cranially and caudally to the segments studied. Stimulation of the dorsolateral tract at a distance of 15–25 mm from the site of recording evoked complex postsynaptic potentials consisting of several successive waves in the motoneurons. The character of the PSPs was not clearly linked with the function of the motoneurons. By their latent periods the components of the PSPs could be placed in three groups. The "primary" components were reproduced in response to stimulation at 50–100/sec whereas the "secondary" and "tertiary" components were weakened or blocked. It is postulated that the "primary" components are evoked through monosynaptic connections between propriospinal fibers of the dorsolateral tract and motoneurons of the forelimb muscles, while the late components are evoked through polysynaptic pathways, including segmental interneurons. Many of these interneurons, located in the ventral horn and intermediate zone, were strongly excited during stimulation of the dorsolateral tract.