Influence of spinal cord compression on the C3–C4 propriospinalneurons in cats

Abstract

The C3–C4 propriospinal neurons (PNs) transmitmotor signals to forelimb motoneurons. Stem axons of thePNs bifurcate in the same segments and send ascending axonsto the lateral reticular nucleus (LRN) as well as descendingaxons to the cervical motor nucleus. After laminectomy ofdecerebrated cats, ascending axons were stimulated by tungstenelectrodes placed in the LRN. The N1 descending incomingvolleys via axon reflexes with a latency of approximately1.5 ms (N1 potential) were recorded in the forelimb motoneuronpools at C8 segment. We compressed the spinal cord at C3or C6 segment by 6 × 5 mm plastic material and analyzedamplitudes of the N1 potentials at C8 motoneuron pools.After spinal compression step by step until 3000μm from thesurface for 30min at the C3 segment, the amplitude of N1potentials decreased to approximately 39.7% of the control.On the other hand, the amplitude of N1 potentials changedlittle after the same compression of the C6 segment. The N1potentials during compression of the C3 segment did not recoverto the initial amplitude of 63.5% after decompression. Itis concluded that activities of axons at C3 segment are moresensitive than those at C6 to compression of the spinal cord.We discuss the properties of the bifurcation of the stem axonsand the central spinal cord injury.