A Simple Cranial Window Technique for Optical Monitoring of Cerebrocortical Microcirculation and NAD/NADH Redox State. Effect of Mitochondrial Electron Transport Inhibitors and Anoxic Anoxia

Abstract: Fluorescence of NADH and vascular volume of the brain cortex of chloralose-anesthetized cats were measured by surface fluororeflectometry. A cranial window and superfusion technique was elaborated for the topical inhibition of mitochondrial electron transport in the brain cortex by amytal (inhibits at site I) and cyanide (inhibits at site III). The changes in NAD/NADH redox state and CVV evoked by these electron transport inhibitors were compared with those elicited by anoxic anoxia. Amytal (10^-3-10^-1 M ) and cyanide (10^-5-10^-2 M ) resulted in a concentration-dependent and reversible increase in cortical NAD reduction and vascular volume, but the cerebrocortical vessels were almost completely dilatated long before maximum NAD reduction was reached. Cyanide at 10^-2 M increased cortical NAD reduction and vascular volume as much as anoxic anoxia. Amytal at 10^-1 M induced approximately half of the NAD reduction evoked by 10^-2 M cyanide or anoxic anoxia, but resulted in only slightly less vasodilatation than that following cyanide and anoxic anoxia. Since amytal inhibits mitochondrial electron transport at site I—and cyanide and anoxia at site III—but induces a comparable degree of vasodilatation, it is concluded that cytochrome oxidase cannot be the single molecular oxygen sensor in the brain cortex.