Bilateral dorsal root potentials in the lower sacral spinal cord.

Bilateral dorsal root potentials (DRPs) evoked in the S3 dorsal roots by stimulation of the S2 and L6 dorsal roots and the cutaneous afferents entering the spinal cord in the lumbar segments have been studied in spinal cats. Stimulation of all these afferents produces DRPs which have the same amplitude on both sides of the spinal cord. During long-lasting repetitive stimulation the negativity of the ipsilateral dorsal root is maintained only when this stimulation is applied to the neighbouring dorsal root. Depression of the testing DRPs produced by preceding single volleys or repetitive stimulation is only slightly larger on the contralateral side of the cord. The difference between depression of the DRPs on both sides of the cord is significantly smaller in the S3 than in the L7 segment. Following conditioning tetanization both ipsi- and contralateral DRPs undergo depression. The pattern of bilateral DRPs in the S3 segment significantly differs from that observed in the L7 segment and these differences correspond to the already known distinct arrangement of the substantia gelatinosa in the two parts of the cord.