DORSAL ROOT POTENTIALS OF THE SPINAL CORD

Abstract

The dorsal root potentials (d.r.p.''s) which are set up in the frog''s spinal cord either by dorsal or by ventral root volleys have been systematically studied. The expts. indicate that 1) the d.r.p. is a catelectrotonic potential propagated electrotonically from a central focus, and is analyzable into an initial active phase and a later phase of passive decay. 2) The d.r.p.''s set up by strong and/or repetitive stimulation with dorsal root volleys have, in addition, a prolonged phase due to inter-nuncial after-discharge, which is increased by the convulsant drugs, strychnine, curarine and veratrine, and diminished by the narcotic, nembutal. 3) Internuncial after-discharge is not effective in prolonging the d.r.p.''s set-up by ventral root volleys, which always show a late phase of passive decay comparable with that of (1) above. 4) Nembutal greatly prolongs (up to 10 times) the time constant of decay of the d.r.p.''s set up by dorsal and ventral root volleys, but has relatively little effect on the rising phases. 5) The d.r.p. recorded in a dorsal root is abolished during the spike of a maximum volley fired in through that root and in part recovers during the decline of the spike, leaving usually 50 to 90% permanently destroyed. 6) The discharges of impulses out along the dorsal root fibres (dorsal root reflex), which often is associated with the d.r.p., has been shown to conform in all respects to the hypothesis that it is secondary to the cathodal polarization of the central terminals of these fibers. An hypothesis is developed which shows how the synaptic poten- tial set up by the trans-synaptic action of the dorsal root volley could secondarily produce the cathodal focus at the terminals of dorsal root fibres, and hence the spreading catelectrotonus of the d.r.p.