Fig. 3.

Changes in carbonic acid buffer species during spreading depression. The uppermost trace shows [H⁺]_o changes after spreading depression elicited by 100 Hz bipolar surface stimulation for 5 s on the parietal cortex. The [H⁺]_o recording was made 300 μm beneath the parietal–pial surface. In this example, [H⁺]_o reached a peak acid level of pH 6.79 before returning to base line. The DC signal (lowermost trace) was recorded from the reference barrel of the H⁺-selective double-barrelled microelectrode. The negative DC shift was used as a time mark to gauge the time to [H⁺]_o, Pt_CO2, or [NH₃] peak changes and their resolution. Pt_CO2 (second trace from the top) was recorded from the adjacent parietal surface. Here Pt_CO2 rose to 79 Torr before returning to base line in a damped oscillatory fashion. ${\left[{\mathrm{HCO}}_3^{-}\right]}_{\mathrm{o}}$ changes (second trace from the bottom) were calculated according to Eq. 4. Solid dots represent specific calculated points. In this example ${\left[{\mathrm{HCO}}_3^{-}\right]}_{\mathrm{o}}$ rose to approximately 52 mM during the alkaline transient () and fell to a low of 13 mM before returning to base line.