Changes in Cortical pH and Blood Flow Accompanying Spreading Cortical Depression and Convulsion

Local changes in cerebral cortex hydrogen ion concentration of as much as 0.5 ph units were observed to accompany the waves of cortical spreading depression or convulsion in cats and rabbits. A diphasic wave consisting of an initial alkaline followed by a more prolonged acid shift was observed in most cases. No significant differences were found between the ph changes accompanying spreading depression and those accompanying spreading convulsion. These ph shifts, like the abnormal ECG activity and the slowly changing potential wave which accompanied them, spread over the surface of the cerebral cortex with a velocity of 1–3 mm/min. The curve of cortical ph change is coincident with, and similar in shape to, the slowly changing potential difference measured between a point on the cortical surface and the jugular blood. For every unit change in ph, the cortex-blood P.D. is shifted approximately 30 mv. It is suggested that the slowly changing potential difference arises across the blood-brain barrier rather t...