EXTEROCEPTIVE AND PROPRIOCEPTIVE ASCENDING IMPULSES IN PYRAMIDAL TRACT OF CAT

Abstract

In a recent exptl. study Brodal and Walberg (Arch. Neurol. Psychiat. 68: 755 (1952)) demonstrated by anatomical methods ascending fibers in the pyramidal tract of the cat. These fibers take origin from all levels of the cord and ascend among the descending fibers in the lateral and ventral cortico-spinal tracts, the pyramids, pons, and capsula interna, and finally reach the cerebral cortex. Another contribution of ascending fibers in the pyramid comes from the nuclei of the dorsal columns. In the present study, cats were anesthetized with Dial, the pyramids exposed by a ventral approach, and an "active" recording electrode placed on 1 pyramid. Different peripheral nerves were stimulated by single square wave shocks, and the ensuing potentials in the pyramid recorded. Potentials were recorded in the pyramid following stimulation of cutaneous, muscular, and mixed nerves. Cutaneous nerve stimulation gave more marked responses than stimulation of muscular nerves. On cutaneous nerve stimulation a positive potential showing 3-4 deflections was constantly obtained. Transection of the pyramid above the recording electrode did not alter the response. Transection of the pyramid below the recording electrode greatly,diminished the responses but did not abolish them. Transections of the dorsal column of the cord on the side of the nerve stimulation reduced the potentials somewhat less than cutting the pyramid. The responses were largest on stimulation of the contralateral forelimb, less from the homolateral forelimb and contralateral hindlimb. From the homolateral hind-limb almost no responses were obtained. It is considered likely that the ascending pyramidal fibers may represent the afferent link in the plantar and abdominal reflexes.