title: Layer-dependent BOLD and CBV-weighted fMRI responses in the rat olfactory bulb.
abstract: The olfactory bulb is a laminarized brain structure involved in odor sensation that has important implications to basic neuroscience research, like mechanisms for neurovascular coupling and early disease diagnosis. To investigate laminar-dependent responses to odor exposure, blood oxygenation level-dependent (BOLD) and cerebral blood volume weighted (CBVw) fMRI with iron oxide nanoparticle contrast agent were obtained with 110×110×500μm(3) resolution in urethane-anesthetized rats at 9.4T. The baseline total CBV is the largest at the olfactory bulb surface and midline, and decreases in the deeper layers, while a band of increased microvasculature density is observed at the glomerular, external plexiform and mitral cell layers. With odor exposure, CBVw fMRI is more sensitive and reproducible than BOLD. BOLD fMRI had the greatest activation on the bulb surface, midline, olfactory nerve and glomerular layers, while CBVw activation peaked in glomerular and external plexiform layers, but was still significant in mitral cell layer. Negative BOLD responses were observed in the bulb midline and near large blood vessels. CBVw laminar profiles are similar to the layer-dependent metabolic changes to the same odor exposure reported by previous glucose metabolism studies. Unique activation patterns for two different odor conditions were also differentiated with CBVw fMRI. Our study suggests that CBVw activation better represents the spatial location of metabolic activity in the olfactory bulb than BOLD.
authors.affiliation: Neuroimaging Laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA, USA. Electronic address: ajp94@pitt.edu.
authors.forename: Alexander John
authors.initials: AJ
authors.lastname: Poplawsky
authors.affiliation: Neuroimaging Laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA, USA; Department of Neurobiology, University of Pittsburgh, Pittsburgh, PA, USA; Center for Neuroscience Imaging Research, Institute of Basic Science (IBS), Sungkyunkwan University, Suwon 440-746, Republic of Korea; Department of Biological Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
authors.forename: Seong-Gi
authors.initials: SG
authors.lastname: Kim
mesh_terms: D000818:Animals; D001810:Blood Volume / Q000502:physiology*; D001921:Brain / Q000033:anatomy & histology; D001931:Brain Mapping; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003627:Data Interpretation, Statistical; D005290:Ferric Compounds; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008833:Microcirculation / Q000502:physiology; D053758:Nanoparticles; D009812:Odorants; D009830:Olfactory Bulb / Q000033:anatomy & histology / Q000098:blood supply / Q000502:physiology*; D010100:Oxygen / Q000097:blood*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012903:Smell / Q000502:physiology*
chemical_list: D005290:Ferric Compounds; C000499:ferric oxide; D010100:Oxygen
keywords: BOLD; Cerebral blood volume (CBV); Functional MRI; Layer dependent; Monocrystalline iron oxide nanoparticles (MION); Olfactory bulb