Functional MRI of somatosensory activation in rat: effect of hypercapnic up-regulation on perfusion- and BOLD-imaging.
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.
Bock
C
C
Max-Planck-Institute for Neurological Research, Cologne, Germany.
Schmitz
B
B
Kerskens
C M
CM
Gyngell
M L
ML
Hossmann
K A
KA
Hoehn-Berlage
M
M
D000818:Animals; D002245:Carbon Dioxide / Q000008:administration & dosage; D002560:Cerebrovascular Circulation; D004558:Electric Stimulation; D005552:Forelimb / Q000502:physiology; D006935:Hypercapnia / Q000378:metabolism / Q000503:physiopathology*; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000378:metabolism / Q000503:physiopathology*; D013382:Subtraction Technique; D015854:Up-Regulation
D002245:Carbon Dioxide; D010100:Oxygen