title: Apparent diffusion time of oxygen from blood to tissue in rat cerebral cortex: implication for tissue oxygen dynamics during brain functions.
abstract: To investigate the dynamics of tissue oxygen demand and supply during brain functions, we simultaneously recorded Po(2) and local cerebral blood flow (LCBF) with an oxygen microelectrode and laser Doppler flowmetry, respectively, in rat somatosensory cortex. Electrical hindlimb stimuli were applied for 1, 2, and 5 s to vary the duration of evoked cerebral metabolic rate of oxygen (CMR(O(2))). The electrical stimulation induced a robust increase in Po(2) (4-9 Torr at peak) after an increase in LCBF (14-26% at peak). A consistent lag of approximately 1.2 s (0.6-2.3 s for individual animals) in the Po(2) relative to LCBF was found, irrespective of stimulus length. It is argued that the lag in Po(2) was predominantly caused by the time required for oxygen to diffuse through tissue. During brain functions, the supply of fresh oxygen further lagged because of the latency of LCBF onset ( approximately 0.4 s). The results indicate that the tissue oxygen supports excess demand until the arrival of fresh oxygen. However, a large drop in Po(2) was not observed, indicating that the evoked neural activity demands little extra oxygen or that the time course of excess demand is as slow as the increase in supply. Thus the dynamics of Po(2) during brain functions predominantly depend on the time course of LCBF. Possible factors influencing the lag between demand and supply are discussed, including vascular spacing, reactivity of the vessels, and diffusivity of oxygen.
authors.affiliation: Department of Radiology and Nuclear Medicine, Akita Research Institute for Brain and Blood Vessels, Akita, Japan. masamoto@nirs.go.jp
authors.forename: Kazuto
authors.initials: K
authors.lastname: Masamoto
authors.forename: Jeff
authors.initials: J
authors.lastname: Kershaw
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Ureshi
authors.forename: Naosada
authors.initials: N
authors.lastname: Takizawa
authors.forename: Hirosuke
authors.initials: H
authors.lastname: Kobayashi
authors.forename: Kazuo
authors.initials: K
authors.lastname: Tanishita
authors.forename: Iwao
authors.initials: I
authors.lastname: Kanno
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology*; D002540:Cerebral Cortex / Q000098:blood supply / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004058:Diffusion; D004558:Electric Stimulation; D007700:Kinetics; D017078:Laser-Doppler Flowmetry; D010092:Oximetry; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D010100:Oxygen