Metabolic brain imaging is widely used to evaluate brain function and disease, and quantitative assays require local retention of compounds used to register changes in cellular activity. As labeled metabolites of [1- and 6-(14)C]glucose are rapidly released in large quantities during brain activation, this study evaluated release of metabolites and proteins through perivascular fluid flow, a pathway that carries solutes from brain to peripheral lymphatic drainage sites. Assays with [3,4-(14)C]glucose ruled out local oxidation of glucose-derived lactate as a major contributor of label loss. Brief infusion of [1-(14)C]glucose and D-[(14)C]lactate into the inferior colliculus of conscious rats during acoustic stimulation labeled the meninges, consistent with perivascular clearance of [(14)C]metabolites from interstitial fluid. Microinfusion of Evans blue albumin and amyloid-beta(1-40) (Abeta) caused perivascular labeling in the inferior colliculus, labeled the surrounding meninges, and Abeta-labeled-specific blood vessels in the caudate and olfactory bulb and was deposited in cervical lymph nodes. Efflux of extracellular glucose, lactate, and Abeta into perivascular fluid pathways is a normal route for clearance of material from the inferior colliculus that contributes to underestimates of brain energetics. Convergence of 'watershed' drainage to common pathways may facilitate perivascular amyloid plaque formation and pathway obstruction in Alzheimer's disease.
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