Influence of spinal cord compression on the C3-C4 propriospinal neurons in cats.

Abstract

The C3-C4 propriospinal neurons (PNs) transmit motor signals to forelimb motoneurons. Stem axons of the PNs bifurcate in the same segments and send ascending axons to the lateral reticular nucleus (LRN) as well as descending axons to the cervical motor nucleus. After laminectomy of decerebrated cats, ascending axons were stimulated by tungsten electrodes placed in the LRN. The N1 descending incoming volleys via axon reflexes with a latency of approximately 1.5 ms (N1 potential) were recorded in the forelimb motoneuron pools at C8 segment. We compressed the spinal cord at C3 or C6 segment by 6 x 5 mm plastic material and analyzed amplitudes of the N1 potentials at C8 motoneuron pools. After spinal compression step by step until 3000 microm from the surface for 30 min at the C3 segment, the amplitude of N1 potentials decreased to approximately 39.7% of the control. On the other hand, the amplitude of N1 potentials changed little after the same compression of the C6 segment. The N1 potentials during compression of the C3 segment did not recover to the initial amplitude of 63.5% after decompression. It is concluded that activities of axons at C3 segment are more sensitive than those at C6 to compression of the spinal cord. We discuss the properties of the bifurcation of the stem axons and the central spinal cord injury.