On the Potential Changes in Spinal Cord During Administration of Carbon Dioxide

1. The changes of root potentials by the administration of carbon dioxide (6.6%-29.8%) was examined on the excised toad's spinal cord. 2. In low concentrations (below 8%) and in early stage of high concentrations of the gas, ventral root potential increases in height and spike (discharges) decreases in number, but the changes of dorsal root potential were hardly observable in these conditions. 3. In later stage of high concentrations (over 8 %), ventral root potential decreases in height and spike discharges superimposed on it also decrease in number. The decrease of dorsal root potentials was observed more later. In the experiment when the concentration was 11 % ventral root potential abolished after 60 minutes. 4. The changes of root potentials were also examined by applying strychnine and polarizing currents to the spinal cord, combined with carbon dioxide or not. From these results, it may be concluded that the blocking action of carbon dioxide is attributable to the hyperpolarization of motoneurons and interneurons.