ELECTRICAL-FIELD DISTRIBUTION WITHIN THE INJURED CAT SPINAL-CORD - INJURY POTENTIALS AND FIELD DISTRIBUTION

This study investigated the spontaneous injury potentials measured aft er contusion or transection injury to the cat spinal cord. In addition , the distribution of electrical field potentials on the surface and w ithin the spinal cord were measured following applied electrical field s after transection and contusion injuries. After transection of the s pinal cord, the injury potentials were -19.8 +/- 2.6 mV; after contusi on of the spinal cord, the injury potentials were -9.5 +/- 2.2 mV. The se potentials returned to control values within 2.5-4 h after injury. The electrical field distribution measured on the dorsal surface, as w ell as within the spinal cord, after the application of a 10 mu A curr ent, showed little difference between contusion and transection injuri es. Scalar potential fields were measured using two configurations of stimulating electrodes: dorsal to dorsal (D-D), in which both electrod es were placed epidurally on the dorsal surface of the spinal cord, an d ventral to dorsal (V-D), in which one electrode was placed dorsally and one ventrally. As reported in normal uninjured cats, the total cur rent in the midsagittal plane for the D-D configuration was largely co nfined to the dorsal portion of the spinal cord; with the V-D configur ation, the current distribution was uniform throughout the spinal cord . In the injured spinal cord, the equipotential lines midway between t he stimulating electrodes have a wider separation than in the uninjure d spinal cord. Because the magnitude of the electrical field E is equa l to the current density J multiplied by the resistivity r, this sugge sts that either the current density is reduced or that the resistivity is reduced.