Regional cerebral blood flow and BOLD responses in conscious and anesthetized rats under basal and hypercapnic conditions: Implications for functional MRI studies

Kenneth Sicard, Qiang Shen, Mathew E. Brevard, Ross Sullivan, Craig F. Ferris, Jean A. King, Timothy Q. Duong

Research output: Contribution to journalArticlepeer-review

201 Scopus citations

Abstract

Anesthetics, widely used in magnetic resonance imaging (MRI) studies to avoid movement artifacts, could have profound effects on cerebral blood flow (CBF) and cerebrovascular coupling relative to the awake condition. Quantitative CBF and tissue oxygenation (blood oxygen level-dependent [BOLD]) were measured, using the continuous arterial-spin-labeling technique with echo-planar-imaging acquisition, in awake and anesthetized (2% isoflurane) rats under basal and hypercapnic conditions. All basal blood gases were within physiologic ranges. Blood pressure, respiration, and heart rates were within physiologic ranges in the awake condition but were depressed under anesthesia (P < 0.05). Regional CBF was heterogeneous with whole-brain CBF values of 0.86 ± 0.25 and 1.27 ± 0.29 mL · g-1 · min-1 under awake and anesthetized conditions, respectively. Surprisingly, CBF was markedly higher (20% to 70% across different brain conditions) under isoflurane-anesthetized condition compared with the awake state (P < 0.01). Hypercapnia decreased pH, and increased PCO2 and PO2. During 5% CO2 challenge, under awake and anesthetized conditions, respectively, CBF increased 51 ± 11% and 25 ± 4%, and BOLD increased 7.3 ± 0.7% and 5.4 ± 0.4%. During 10% CO2 challenge, CBF increased 158 ± 28% and 47 ± 11%, and BOLD increased 12.5 ± 0.9% and 7.2 ± 0.5%. Since CBF and BOLD responses were substantially higher under awake condition whereas blood gases were not statistically different, it was concluded that cerebrovascular reactivity was suppressed by anesthetics. This study also shows that perfusion and perfusion-based functional MRI can be performed in awake animals.

Original languageEnglish (US)
Pages (from-to)472-481
Number of pages10
JournalJournal of Cerebral Blood Flow and Metabolism
Volume23
Issue number4
DOIs
StatePublished - Apr 1 2003

Keywords

  • Anesthesia
  • Awake animals
  • CBF
  • Carbon dioxide
  • Spin labeling
  • fMRI

ASJC Scopus subject areas

  • Neurology
  • Clinical Neurology
  • Cardiology and Cardiovascular Medicine

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