title: Vasodilation Mechanism of Cerebral Microvessels Induced by Neural Activation under High Baseline Cerebral Blood Flow Level Results from Hypercapnia in Awake Mice.
abstract: OBJECTIVE
  We investigated the effects of the baseline CBF level at resting state on neurovascular coupling.
  
  
  METHODS
  Diameters of arterioles, capillaries, and venulas in awake mouse brain were measured by a two-photon microscope. Vasodilation in each of the cerebral vessels was caused by three experimental conditions: (1) sensory stimulation, (2) 5% CO2 inhalation (hypercapnia), (3) simultaneous exposure to sensory stimulation and 5% CO2 inhalation. CBF and CBV were also measured by a microscope and a CCD camera.
  
  
  RESULTS
  Increases in CBF and CBV were observed under all experimental conditions. After the increases in CBF and CBV due to hypercapnia, additional increases in CBF and CBV occurred during sensory stimulation. Diameter changes in arterioles were significantly larger than those in capillaries and venulas under both sensory stimulation and 5% CO2 inhalation. Additional vasodilation from sensory stimulation was observed under hypercapnia. The diameter change in each vessel type during sensory stimulation was maintained under simultaneous exposure to sensory stimulation and hypercapnia.
  
  
  CONCLUSIONS
  The diameter change of cerebral vessels during neural activation is reproducible regardless of whether baseline CBF has increased or not. Our finding directly demonstrates the concept of uncoupling between energy consumption and energy supply during cortical activation.
authors.affiliation: Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Asuka
authors.initials: A
authors.lastname: Nishino
authors.affiliation: Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Takuwa
authors.affiliation: Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Urushihata
authors.affiliation: Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan.|Advanced Clinical Research Center, Fukushima Global Medical Science Center, Fukushima Medical University, Fukushima, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ito
authors.affiliation: Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Ikoma
authors.affiliation: Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan.|Laboratory of Behavioral Physiology, Faculty of Engineering, Iwate University, Morioka, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Matsuura
mesh_terms: D000818:Animals; D001160:Arterioles / Q000503:physiopathology; D001783:Blood Flow Velocity; D001921:Brain / Q000098:blood supply* / Q000503:physiopathology*; D002196:Capillaries / Q000503:physiopathology; D002560:Cerebrovascular Circulation; D006935:Hypercapnia / Q000503:physiopathology*; D008297:Male; D051379:Mice; D014851:Wakefulness
keywords: cerebral blood flow; hypercapnia; neurovascular coupling; two-photon imaging; vasodilation