Brain NADH redox state monitored in vivo by fiber optic surface fluorometry.
A new approach for the evaluation of brain energy metabolism in awake animals became possible as UV transmitting optical fibers became available. A variety of surface fiber optic fluorometers / reflectometers which were developed during the past decade enabled the monitoring of intramitochondrial NADH redox state in unanesthetized animals. The bundle of flexible fibers was connected to the brain via a cemented light guide holder implanted epidurally. The two signals obtained, 366 nm reflectance and 450 nm fluorescence, are subjected to various artifacts not connected to the intramitochondrial NADH redox state. In our system, the effects of movement artifacts and changes in blood oxygenation are negligible while the effects of tissue absorption or blood volume changes are considerable and could be minimized by subtraction of the two signals (1:1 ratio) providing the corrected fluorescence signal. The brain was exposed to various physiological and pathological conditions which resulted in the increase or decrease in the level of NADH. Under anoxia, hypoxia and ischemia, oxygen availability decreased and the metabolic state of the brain became more reduced (state 4-5 transition). When the brain was activated by seizures, spreading depression of hyperbaric oxygenation NADH became more oxidized (state 4-3 transition).