PHYSIOLOGICAL STIMULATION INCREASES NONOXIDATIVE GLUCOSE-METABOLISM IN THE BRAIN OF THE FREELY MOVING RAT

The effects of mild stress on nonoxidative glucose metabolism were studied in the brain of the freely moving rat. Extracellular lactate levels in the hippocampus and striatum were monitored at 2.5-min intervals with microdialysis coupled with an enzyme-based flow injection analysis system. Ten minutes of restraint stress led to a 235% increase in extracellular lactate levels in the striatum. A 5-min tail pinch caused an increase of 193% in the striatum and 170% in the hippocampus. Local application of tetrodotoxin in the striatum blocked the rise in lactate following tail pinch and inhibited the subsequent clearance of lactate from the extracellular fluid. Local application of the noncompetitive N-methyl-D-aspartate receptor antagonist MK-801 had no effect on the tail pinch-stimulated increase in lactate in the striatum. These results show that mild physiological stimulation can lead to a rapid increase in nonoxidative glucose metabolism in the brain.