Development of coritcospinal effects on forelimb motor control.

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We studied on the role and mechanism of the corticospinal tract in the spinal motor center in the cat and immature rat.(1) We examined the effect of stimulation of the pyramidal tract using electromyographic recordings from forelimb muscles and intracellular recordings from their innervating motoneurones in the decerebrated cat. Muscle activities were evoked exclusively in the flexor muscle and they were most prominent in the flexor phase during locomotion. The excitatory effect from the corticospinal tract would be transmitted disynaptically to the motoneurone. Furthermore, we suggested in the experiment of the partial lesion of the spinal cord that the pathway conveying the corticospinal effect was different in motoneurones innervating distant and proximal muscles.(2) We examined pharmacologically on the synaptic transmission from corticospinal fibers to motoneurones using the slice preparation of the cervical spinal cord of the immature rat. We revealed that the corticospinal tract fibers in the dorsal funiculus could be selectively stimulated in the slice preparation. The pathway was transmitted by both NMDA and nonNMDA receptors and modulated by glycinergic inhibition.(3) The cerebral cortex or the thoracic spinal cord were removed from the newborn rat, and the respective tissue from the embryo was transplanted. One to four months after the transplant, we obtained the preliminary result of changes in the locomotor pattern which was analyzed by recordings of the foot print from each foot in the spinal cord transplanted preparation.