Measurements of regional cortical blood flow during changes in extracellular potassium activity evoked by direct cortical stimulation in the primate

Abstract

In the normal cerebral cortex of eight baboons anesthetized with α-chloralose, we recorded simultaneously extracellular potassium activity (K e) by ion-exchanger microelectrodes and tissue blood flow by hydrogen clearance in the same region, and measured the changes in these variables following direct electrical stimulation of the cortex locally. Stimulation elicited a period (10 to 40 s) of seizure activity with K e increasing to a mean value of 9.5 m m, followed by prompt decay to below the prestimulus value (the undershoot) before this baseline was finally regained during the next few minutes. The K e increase was accompanied by a significant ( P < 0.002) increase in flow, in all animals, from a mean value of 92 ml/100 g/min (control) to one of 173 ml/100 g/min; there was a significant correlation between the peak increases in K e and flow. In three animals, this hyperemia was preceded by a brief (5 to 15-s) decrease in flow, averaging 43% of control. A prolonged reduction in flow to a mean of 42 ml/100 g/min, significantly below control ( P < 0.03), accompanied K e undershoot in six animals, with subsequent restoration of normal flow. Systemic blood pressure was unaffected throughout this sequence, indicating that the flow changes resulted from local vasodilation and vasoconstriction in the hyperemic and undershoot phases, respectively. We discuss the possibility that the flow reduction during the K e undershoot resulted from a reduction in local metabolic rate and, considering an alternative explanation in terms of the vasoactive effects of local ion concentrations, conclude that the decrease in K e was not by itself likely to have produced this flow reduction.