title: Effects of the α₂-adrenergic receptor agonist dexmedetomidine on neural, vascular and BOLD fMRI responses in the somatosensory cortex.
abstract: This article describes the effects of dexmedetomidine (DEX) - the active ingredient of medetomidine, which is the latest popular sedative for functional magnetic resonance imaging (fMRI) in rodents - on multiple unit activity, local field potential (LFP), cerebral blood flow (CBF), pial vessel diameter [indicative of cerebral blood volume (CBV)], and blood oxygenation level-dependent (BOLD) fMRI. These measurements were obtained from the rat somatosensory cortex during 10 s of forepaw stimulation. We found that the continuous intravascular systemic infusion of DEX (50 μg/kg/h, doses typically used in fMRI studies) caused epileptic activities, and that supplemental isoflurane (ISO) administration of ~0.3% helped to suppress the development of epileptic activities and maintained robust neuronal and hemodynamic responses for up to 3 h. Supplemental administration of N(2)O in addition to DEX nearly abolished hemodynamic responses even if neuronal activity remained. Under DEX + ISO anesthesia, spike firing rate and the delta power of LFP increased, whereas beta and gamma power decreased, as compared with ISO-only anesthesia. DEX administration caused pial arteries and veins to constrict nearly equally, resulting in decreases in baseline CBF and CBV. Evoked LFP and CBF responses to forepaw stimulation were largest at a frequency of 8-10 Hz, and a non-linear relationship was observed. Similarly, BOLD fMRI responses measured at 9.4 T were largest at a frequency of 10 Hz. Both pial arteries and veins dilated rapidly (artery, 32.2%; vein, 5.8%), and venous diameter returned to baseline slower than arterial diameter. These results will be useful for designing, conducting and interpreting fMRI experiments under DEX sedation.
authors.affiliation: Neuroimaging Laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA, USA. mif5@pitt.edu
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Fukuda
authors.forename: Alberto L
authors.initials: AL
authors.lastname: Vazquez
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Zong
authors.forename: Seong-Gi
authors.initials: SG
authors.lastname: Kim
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000627:therapeutic use; D000818:Animals; D058256:Brain Waves / Q000187:drug effects*; D002536:Cerebral Arteries / Q000502:physiology; D002550:Cerebral Veins / Q000502:physiology; D020927:Dexmedetomidine / Q000494:pharmacology*; D004827:Epilepsy / Q000139:chemically induced / Q000188:drug therapy; D006614:Hindlimb / Q000294:innervation; D007530:Isoflurane / Q000494:pharmacology / Q000627:therapeutic use; D008279:Magnetic Resonance Imaging; D008297:Male; D009569:Nitric Oxide / Q000494:pharmacology; D010100:Oxygen / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000098:blood supply / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D018685:Anesthetics, Inhalation; D009569:Nitric Oxide; D020927:Dexmedetomidine; D007530:Isoflurane; D010100:Oxygen