title: Two-photon NADH imaging exposes boundaries of oxygen diffusion in cortical vascular supply regions.
abstract: Oxygen transport imposes a possible constraint on the brain's ability to sustain variable metabolic demands, but oxygen diffusion in the cerebral cortex has not yet been observed directly. We show that concurrent two-photon fluorescence imaging of endogenous nicotinamide adenine dinucleotide (NADH) and the cortical microcirculation exposes well-defined boundaries of tissue oxygen diffusion in the mouse cortex. The NADH fluorescence increases rapidly over a narrow, very low pO(2) range with a p(50) of 3.4 ± 0.6 mm Hg, thereby establishing a nearly binary reporter of significant, metabolically limiting hypoxia. The transient cortical tissue boundaries of NADH fluorescence exhibit remarkably delineated geometrical patterns, which define the limits of tissue oxygen diffusion from the cortical microcirculation and bear a striking resemblance to the ideal Krogh tissue cylinder. The visualization of microvessels and their regional contribution to oxygen delivery establishes penetrating arterioles as major oxygen sources in addition to the capillary network and confirms the existence of cortical oxygen fields with steep microregional oxygen gradients. Thus, two-photon NADH imaging can be applied to expose vascular supply regions and to localize functionally relevant microregional cortical hypoxia with micrometer spatial resolution.
authors.affiliation: Department of Neurology, Center for Neural Development and Disease, University of Rochester Medical Center, Rochester, New York 14642, USA. karl_kasischke@urmc.rochester.edu
authors.forename: Karl A
authors.initials: KA
authors.lastname: Kasischke
authors.forename: Elton M
authors.initials: EM
authors.lastname: Lambert
authors.forename: Ben
authors.initials: B
authors.lastname: Panepento
authors.forename: Anita
authors.initials: A
authors.lastname: Sun
authors.forename: Harris A
authors.initials: HA
authors.lastname: Gelbard
authors.forename: Robert W
authors.initials: RW
authors.lastname: Burgess
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Foster
authors.forename: Maiken
authors.initials: M
authors.lastname: Nedergaard
mesh_terms: D015502:Absorptiometry, Photon; D000465:Algorithms; D000818:Animals; D015687:Cell Hypoxia / Q000502:physiology; D002533:Cerebral Angiography; D002540:Cerebral Cortex / Q000098:blood supply* / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004058:Diffusion; D055724:Electrophysiological Phenomena; D002534:Hypoxia, Brain / Q000473:pathology; D007091:Image Processing, Computer-Assisted; D051379:Mice; D008810:Mice, Inbred C57BL; D008833:Microcirculation / Q000502:physiology; D009243:NAD / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010812:Physical Stimulation; D010841:Pia Mater / Q000033:anatomy & histology / Q000098:blood supply; D013003:Somatosensory Cortex / Q000033:anatomy & histology / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014738:Vibrissae / Q000502:physiology
chemical_list: D009243:NAD