Effects of Carbon Dioxide on Brain Excitability and Electrolytes

¹ From the Department of Pharmacology, University of Utah College of Medicine, Salt Lake City, Utah

Effects of various concentrations of CO₂ on brain excitability and electrolyte distribution in rats were studied, and also some properties of seizures induced by abrupt withdrawal from high concentrations of CO₂. Inhalation of relatively low concentrations of CO₂ (5–20%) decreases brain excitability, as measured by an increase in electroshock seizure threshold (EST). In moderately high concentrations (25–40%), CO₂ increases brain excitability, as measured by a decrease in EST and the appearance of spontaneous seizures. Inhalation of high concentration of CO₂ (40% or higher) markedly decreases brain excitability and causes anesthesia. Thus the effect of CO₂ on brain excitability is related to the concentration inhaled. Abrupt removal of rats from high (anesthetic) concentrations of CO₂ results in spontaneous clonic seizures within 30 seconds to 1 minute after withdrawal; these seizures last for 1–2 minutes. Inhalation of 50% CO₂ decreases brain intracellular Na and K concentrations and produces a marked cellular acidosis. Thirty seconds after abrupt withdrawal of rats from 50% CO₂, but prior to the onset of seizures, the concentration of Na in brain cells increases and the concentration of K decreases.