Multisite Measurements of NADH Redox State from Cerebral Cortex of the Awake Animal

Abstract

There are few non-destructive non-invasive approaches to the study of cortical oxidative metabolism. Nevertheless, the great necessity for the development and application of such approaches arises from the inadequacy of cell and brain slice models on the one hand and the need for interpretive monitoring of brain metabolism in humans, or if possible, under non-operative conditions. Two techniques can be used to study metabolism of the brain without the necessity of an operation, ³¹P NMR which is totally non-invasive and positron emission tomography which requries injection and delivery of the radio isotope. Neither of these methods affords an adequately sharp localization to provide better than regional localization (lam) under current conditions of development and application, on the other hand, when the subject is sacrificed and autoradiography of tritium labelled deoxyglucose is employed, a high degree of metabolic resolution can be obtained albeit the method averages events over times as long as 45 minutes. The need for a non-destructive continuous read out method for brain metabolism providing a high degree of localization, both spacially and within appropriate metabolic compartments is obtained with the fluorescence of mitochondrial pigments, NADH or flavoprotein. Furthermore, this method is applicable as well to frozen tissue surfaces affording high resolution 3D spacial resolution. The discovery that mitochondrial NADH is fluorescent and that the fluorescence is enhanced 15 or more times over that of the pigment in solution afforded a unique “look” at metabolic events in the matrix base of mitochondria; the NADPH therein was found not to respond to variations of electron transport in the respiratory chain (1–3). Furthermore, comparisons of changes of NADH fluorescence could be well correlated with actual tissue assays of NADH in heart and liver (4,5).