CORD POTENTIALS IN SPINAL SHOCK CROSSED EFFECTS IN MONKEY, MACACA MULATTA

Abstract

In the spinal Macaca mulatta monkey the contralateral component of the intermediary cord potential is scarcely detectable in the acute preparation, is small at 12 days after transection but has attained the magnitude of the ipsilateral component within two months. In the chronically hemisected, acutely transected animal, the ipsilateral potential spreads farther up the cord when the stimulus is applied to afferents of the chronic side than when to those of the acute side. When the chronic side is stimulated, the threshold for the crossed cord potential is far higher and its latency far longer than that for the potential on the side of stimulation. When afferents of the acute side are stimulated, the thresholds for ipsilateral and contralateral potentials may be identical and the latter potential may approximate the magnitude of the former. From these data the following conclusions are drawn: 1. The contralateral cord potential is associated with the activity of perikarya or dendrites and not merely with that of axones. 2. Block of the crossed cord potential is due to a high threshold of the cells of the contralateral dorsal horn and not to lack of impulses playing upon them. 3. The above data yield evidence of the internuncial origin of the cord potential. In the cat crossed inhibition of the internuncial potential parallels that of the flexor reflex, though usually it is somewhat less intense. In the chronic monkey, on the other hand, crossed inhibition of the reflex may occur without reduction of the corresponding cord potential. This indicates a locus of inhibition downstream from the internuncials recorded[long dash]presumably at the cells of the anterior horn.