Cerebral Cortex Advance Access originally published online on May 26, 2006
Cerebral Cortex 2007 17(4):942-950; doi:10.1093/cercor/bhl005
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Relationship between Neural, Vascular, and BOLD Signals in Isoflurane-Anesthetized Rat Somatosensory Cortex
Departments of Radiology and Neurobiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
Address correspondence to Seong-Gi Kim, PhD, Department of Radiology, University of Pittsburgh, 3025 East Carson Street, Pittsburgh, PA 15203, USA. Email: kimsg{at}pitt.edu.
Functional magnetic resonance imaging (fMRI) in anesthetized rodents has been commonly performed with 
-chloralose, which can be used only for terminal experiments. To develop a survival fMRI protocol, an isoflurane (ISO) -anesthetized rat model was systematically evaluated by simultaneous measurements of field potential (FP) and cerebral blood flow (CBF) in the somatosensory cortex. A conventional forepaw stimulation paradigm with 0.3 ms pulse width, 1.2 mA current, and 3 Hz frequency induced 54% less evoked FP and 84% less CBF response under ISO than -chloralose. To improve stimulation-induced responses under ISO, 10-pulse stimulations were performed with variations of width, current, and frequency. For widths of 0.1–5.0 ms and currents of 0.4–2.0 mA, evoked FP and CBF increased similarly and reached a plateau. The evoked FP increased monotonically for intervals from 50 to 500 ms, but the CBF peaked at an interval of 83 ms (
12 Hz frequency). These data suggest that different anesthetics profoundly affect FP and CBF responses in different ways, which requires optimizing stimulation parameters for each anesthetic. With the refined stimulation parameters, fMRI consistently detected a well-localized activation focus at the primary somatosensory cortex in ISO-anesthetized rats. Thus, the ISO-anesthetized rat model can be used for cerebrovascular activation studies, allowing repeated noninvasive survival experiments.
Key Words: anesthesia • frequency tuning • laser Doppler flowmetry • local field potential • longitudinal fMRI • neurovascular coupling