title: "Overshoot" of O₂ is required to maintain baseline tissue oxygenation at locations distal to blood vessels.
abstract: In vivo imaging of cerebral tissue oxygenation is important in defining healthy physiology and pathological departures associated with cerebral disease. We used a recently developed two-photon microscopy method, based on a novel phosphorescent nanoprobe, to image tissue oxygenation in the rat primary sensory cortex in response to sensory stimulation. Our measurements showed that a stimulus-evoked increase in tissue pO₂ depended on the baseline pO₂ level. In particular, during sustained stimulation, the steady-state pO₂ at low-baseline locations remained at the baseline, despite large pO₂ increases elsewhere. In contrast to the steady state, where pO₂ never decreased below the baseline, transient decreases occurred during the "initial dip" and "poststimulus undershoot." These results suggest that the increase in blood oxygenation during the hemodynamic response, which has been perceived as a paradox, may serve to prevent a sustained oxygenation drop at tissue locations that are remote from the vascular feeding sources.
authors.affiliation: Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02114, USA. adevor@ucsd.edu
authors.forename: Anna
authors.initials: A
authors.lastname: Devor
authors.forename: Sava
authors.initials: S
authors.lastname: Sakadzic
authors.forename: Payam A
authors.initials: PA
authors.lastname: Saisan
authors.forename: Mohammad A
authors.initials: MA
authors.lastname: Yaseen
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Roussakis
authors.forename: Vivek J
authors.initials: VJ
authors.lastname: Srinivasan
authors.forename: Sergei A
authors.initials: SA
authors.lastname: Vinogradov
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Rosen
authors.forename: Richard B
authors.initials: RB
authors.lastname: Buxton
authors.forename: Anders M
authors.initials: AM
authors.lastname: Dale
authors.forename: David A
authors.initials: DA
authors.lastname: Boas
mesh_terms: D000818:Animals; D001931:Brain Mapping / Q000379:methods; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D010100:Oxygen / Q000097:blood*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000098:blood supply / Q000378:metabolism*
chemical_list: D010100:Oxygen