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  • Title: Functional MRI of somatosensory activation in rat: effect of hypercapnic up-regulation on perfusion- and BOLD-imaging.
    Author: Bock C, Schmitz B, Kerskens CM, Gyngell ML, Hossmann KA, Hoehn-Berlage M.
    Journal: Magn Reson Med; 1998 Mar; 39(3):457-61. PubMed ID: 9498602.
    Abstract:
    Functional activation of somatosensory cortex was studied in alpha-chloralose anesthetized rats by functional magnetic resonance imaging (fMRI), using both perfusion-weighted and T2*-weighted (blood oxygenation level dependent, BOLD) imaging. The sensitivity of functional activation was altered by ventilating animals for 3 minutes with 6% CO2. Before hypercapnic conditioning, electrical stimulation of the left forepaw at a frequency of 3 Hz led to an increase of signal intensity (relative to the unstimulated baseline condition) in the right somatosensory cortex by 6+/-2% (means+/-SD) in T2*-weighted images and by 45%+/-48% in perfusion-weighted images. After hypercapnic conditioning the signal intensity increase in perfusion-weighted images doubled to 91%+/-62% (P=0.034), whereas that of T2*-weighted images only marginally increased to 7+/-4% (not significant). This different behavior in both imaging modalities is interpreted as evidence for an increased flow response in combination with a higher oxygen extraction. Thus, the fMRI data reflect hypercapnia-induced resetting of the functional-metabolic coupling of the tissue during activation.
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