Imaging oxygen consumption in forepaw somatosensory stimulation in rats under isoflurane anesthesia.
The cerebral metabolic rate of oxygen (CMRO2) was dynamically evaluated on a pixel-by-pixel basis in isoflurane-anesthetized and spontaneously breathing rats following graded electrical somatosensory forepaw stimulations (4, 6, and 8 mA). In contrast to alpha-chloralose, which is the most widely used anesthetic in forepaw-stimulation fMRI studies of rats under mechanical ventilation, isoflurane (1.1-1.2%) provided a stable anesthesia level over a prolonged period, without the need to adjust the ventilation volume/rate or sample blood gases. Combined cerebral blood flow signals (CBF) and blood oxygenation level-dependent (BOLD) fMRI signals were simultaneously measured with the use of a multislice continuous arterial spin labeling (CASL) technique (two-coil setup). CMRO2 was calculated using the biophysical BOLD model of Ogawa et al. (Proc Natl Acad Sci USA 1992;89:5951-5955). The stimulus-evoked BOLD percent changes at 4, 6, and 8 A were, respectively, 0.5% +/- 0.2%, 1.4% +/- 0.3%, and 2.0% +/- 0.3% (mean +/- SD, N = 6). The CBF percent changes were 23% +/- 6%, 58% +/- 9%, and 87% +/- 14%. The CMRO2 percent changes were 14% +/- 4%, 24% +/- 6%, and 43% +/- 11%. BOLD, CBF, and CMRO2 activations were localized to the forepaw somatosensory cortices without evidence of plateau for oxygen consumption, indicative of partial coupling of CBF and CMRO2. This study describes a useful forepaw-stimulation model for fMRI, and demonstrate that CMRO2 changes can be dynamically imaged on a pixel-by-pixel basis in a single setting with high spatiotemporal resolution.
Center for Comparative NeuroImaging, Department of Psychiatry, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA. timothy.duong@umassmed.edu
Zhaohui M
ZM
Liu
Karl F
KF
Schmidt
Kenneth M
KM
Sicard
Timothy Q
TQ
Duong
D018685:Anesthetics, Inhalation / Q000008:administration & dosage; D000818:Animals; D001921:Brain / Q000378:metabolism*; D001931:Brain Mapping; D002560:Cerebrovascular Circulation; D004558:Electric Stimulation; D005552:Forelimb / Q000294:innervation*; D007530:Isoflurane / Q000008:administration & dosage; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012119:Respiration; D012121:Respiration, Artificial; D013113:Spin Labels
D018685:Anesthetics, Inhalation; D013113:Spin Labels; D007530:Isoflurane; D010100:Oxygen