CORD POTENTIALS IN SPINAL SHOCK SINGLE VOLLEYS

Abstract

In cats, dogs, and monkeys (Macaca mulatto), cord potentials and reflex responses to single afferent volleys were recorded at intervals after spinal transection ranging from a few secs. to 2 mos. The latency of the cord potential is independent of the strength of the stimulus and long enough to indicate an internuncial origin. The effect of transection upon the cord potential is to reduce the amplitude and spread of the negative components and to abolish or almost abolish the positive components. These effects are far more severe and prolonged in the monkey than in the cat or the dog. In the cat and the dog, the threshold for cord potential and ipsilateral flexor reflex sampled in semitendinosus are equal and fall progressively during the first hour after transection at the end of which they approximate that of the afferent nerve. In the monkey, on the other hand, though the cord potential threshold approximates that of the nerve within 6 hrs., the reflex threshold for semitendinosus requires 12 days or longer to attain that level. Reflex responses from this muscle were never observed even to maximal stimulation in an acutely spinal monkey. On the other hand, stimulation of dorsal roots has given feeble toe flexion and slight tail movement at thresholds approximating those of cord potential and afferent nerve in an acute expt. Hence, in the cat and the dog, spinal shock was demonstrated only at the internuncial level. In the monkey, on the other hand, in addition to more severe internuncial depression, there is evidence of deep and prolonged shock to the motoneurones.