Near-simultaneous hemoglobin saturation and oxygen tension maps in the mouse cortex during amphetamine stimulation.

Abstract

Changes in neuronal activity lead to changes in oxygen consumption, glucose uptake, and blood flow in the brain. While a regional coupling between blood flow and oxygen consumption is generally observed during resting conditions, focal increases in neuronal activity may result in disproportionately larger increases in blood flow to the activated region.1 This alters the oxygenation state of blood and is thought to be the basis of functional activation using nuclear magnetic resonance imaging (f-MRI)2,3 and optical imaging using intrinsic signals.4,5 While f-MRI has become increasingly popular for studying functional activation in the human cortex, the physiologic events underlying the observed signal changes remain poorly characterized and controversial.6,7 In particular, the important dynamic relationship between the oxygen saturation of hemoglobin (SO2) and the blood oxygen tension (PO2) during activation has not been adequately addressed. In this study, we describe, the application of a new type of intravital microscope, using acoustooptic tunable filters (AOTFs),8–10 to the generation of both SO2 and PO2 maps at high-resolution in the cerebral cortex of mice during global neuronal activation by amphetamine administration. SO2 maps are generated from the spectral analysis of reflected absorbance images collected at different wavelengths and PO2 maps are generated from the phosphorescence lifetimes of an injected palladium-porphyrin compound using a frequency-domain measurement.