On-line monitoring of extracellular brain glucose using microdialysis and a NADPH-linked enzymatic assay

A method to monitor extracellular glucose in freely moving rats, based on intracerebral microdialysis coupled to an enzyme reactor is described. The dialysate is continuously mixed with a solution containing the enzymes hexokinase and glucose-6-phosphate dehydrogenase, and the fluorescence of NADPH formed enables the on-line registration of extracellular glucose. The method is applied to monitor changes in extracellular brain glucose during the infusion of glucose, electrically induced seizure, immobilization stress, and repetitive hypoxia. After glucose loading or after seizure, hippocampus dialysate glucose concentration was increased transiently. During immobilization, there was a short-lasting decrease and, thereafter, an increase in the extracellular hippocampus glucose. During repetitive hypoxia in rats with a unilaterally occluded carotid artery, the content of glucose of striatal dialysates followed closely changes in blood pressure. These results illustrate the usefulness of the method in studying changes in brain glucose concentrations under pathological and physiological conditions.